diff --git a/README.md b/README.md
index 071c77636..7590014ff 100644
--- a/README.md
+++ b/README.md
@@ -108,7 +108,9 @@ At bottom of the page, the download button is available for downloading benchmar
 ### Alert comment on commit page
 
 This action can raise [an alert comment][alert-comment-example]. to the commit when its benchmark
-results are worse than previous exceeding a specified threshold.
+results are worse than previous exceeding a specified threshold. If negative the threshold will alert
+if the benchmark result decreases over the specified threshold, and if positive it will alert if the
+benchmark result increase over the specified threshold.
 
 ![alert comment](https://raw.githubusercontent.com/rhysd/ss/master/github-action-benchmark/alert-comment.png)
 
@@ -184,8 +186,10 @@ The step which runs `github-action-benchmark` does followings:
    the workflow fails and the failure is notified to you
 
 By default, this action marks the result as performance regression when it is worse than the previous
-exceeding 200% threshold. For example, if the previous benchmark result was 100 iter/ns and this time
-it is 230 iter/ns, it means 230% worse than the previous and an alert will happen. The threshold can
+exceeding 200% threshold. For example, if the previous benchmark result was 100 ns and this time
+it is 230 ns, it means 230% worse than the previous and an alert will happen. If the threshold specified is negative it
+will alert when the benchmark result decreases, so if the previous benchmark result was 230 ops/ns and this time
+it is 100 ops/ns, if the threshold is set to -200% then an alert will happen. The threshold can
 be changed by `alert-threshold` input.
 
 A live workflow example is [here](.github/workflows/minimal.yml). And the results of the workflow can
diff --git a/src/config.ts b/src/config.ts
index d1a4919b8..5caceac0b 100644
--- a/src/config.ts
+++ b/src/config.ts
@@ -210,7 +210,7 @@ function validateAlertThreshold(alertThreshold: number | null, failThreshold: nu
     if (alertThreshold === null) {
         throw new Error("'alert-threshold' input must not be empty");
     }
-    if (failThreshold && alertThreshold > failThreshold) {
+    if (failThreshold && Math.abs(alertThreshold) > Math.abs(failThreshold)) {
         throw new Error(
             `'alert-threshold' value must be smaller than 'fail-threshold' value but got ${alertThreshold} > ${failThreshold}`,
         );
diff --git a/src/write.ts b/src/write.ts
index d55bb1fa2..28ede811f 100644
--- a/src/write.ts
+++ b/src/write.ts
@@ -103,14 +103,14 @@ function findAlerts(curSuite: Benchmark, prevSuite: Benchmark, threshold: number
             continue;
         }
 
-        const ratio = biggerIsBetter(curSuite.tool)
+        const ratio = biggerIsBetter(curSuite.tool) || threshold < 0
             ? prev.value / current.value // e.g. current=100, prev=200
             : current.value / prev.value; // e.g. current=200, prev=100
 
-        if (ratio > threshold) {
+        if (ratio > Math.abs(threshold)) {
             core.warning(
                 `Performance alert! Previous value was ${prev.value} and current value is ${current.value}.` +
-                    ` It is ${ratio}x worse than previous exceeding a ratio threshold ${threshold}`,
+                    ` It is ${ratio}x worse than previous exceeding a ratio threshold ${Math.abs(threshold)}`,
             );
             alerts.push({ current, prev, ratio });
         }
@@ -272,6 +272,8 @@ async function handleComment(benchName: string, curSuite: Benchmark, prevSuite:
 
 async function handleAlert(benchName: string, curSuite: Benchmark, prevSuite: Benchmark, config: Config) {
     const { alertThreshold, githubToken, commentOnAlert, failOnAlert, alertCommentCcUsers, failThreshold } = config;
+    const absAlertThreshold = Math.abs(alertThreshold);
+    const absFailThreshold = Math.abs(failThreshold);
 
     if (!commentOnAlert && !failOnAlert) {
         core.debug('Alert check was skipped because both comment-on-alert and fail-on-alert were disabled');
@@ -285,7 +287,7 @@ async function handleAlert(benchName: string, curSuite: Benchmark, prevSuite: Be
     }
 
     core.debug(`Found ${alerts.length} alerts`);
-    const body = buildAlertComment(alerts, benchName, curSuite, prevSuite, alertThreshold, alertCommentCcUsers);
+    const body = buildAlertComment(alerts, benchName, curSuite, prevSuite, absAlertThreshold, alertCommentCcUsers);
     let message = body;
     let url = null;
 
@@ -301,8 +303,8 @@ async function handleAlert(benchName: string, curSuite: Benchmark, prevSuite: Be
     if (failOnAlert) {
         // Note: alertThreshold is smaller than failThreshold. It was checked in config.ts
         const len = alerts.length;
-        const threshold = floatStr(failThreshold);
-        const failures = alerts.filter((a) => a.ratio > failThreshold);
+        const threshold = floatStr(absFailThreshold);
+        const failures = alerts.filter((a) => a.ratio > absFailThreshold);
         if (failures.length > 0) {
             core.debug('Mark this workflow as fail since one or more fatal alerts found');
             if (failThreshold !== alertThreshold) {
@@ -312,7 +314,7 @@ async function handleAlert(benchName: string, curSuite: Benchmark, prevSuite: Be
             throw new Error(message);
         } else {
             core.debug(
-                `${len} alerts exceeding the alert threshold ${alertThreshold} were found but` +
+                `${len} alerts exceeding the alert threshold ${absAlertThreshold} were found but` +
                     ` all of them did not exceed the failure threshold ${threshold}`,
             );
         }
diff --git a/test/write.spec.ts b/test/write.spec.ts
index 5cf224525..5df338d8d 100644
--- a/test/write.spec.ts
+++ b/test/write.spec.ts
@@ -377,6 +377,44 @@ describe.each(['https://github.com', 'https://github.enterprise.corp'])('writeBe
                     'CC: @user',
                 ],
             },
+            {
+                it: 'raises an alert when exceeding threshold negative 2.0',
+                config: { ...defaultCfg, alertThreshold: -2.0, failThreshold: -2.0 },
+                data: {
+                    lastUpdate,
+                    repoUrl,
+                    entries: {
+                        'Test benchmark': [
+                            {
+                                commit: commit('prev commit id'),
+                                date: lastUpdate - 1000,
+                                tool: 'jmh',
+                                benches: [bench('bench_fib_10', 100), bench('bench_fib_20', 10000)],
+                            },
+                        ],
+                    },
+                },
+                added: {
+                    commit: commit('current commit id'),
+                    date: lastUpdate,
+                    tool: 'go',
+                    benches: [bench('bench_fib_10', 20), bench('bench_fib_20', 25000)], // Exceeds -2.0 threshold
+                },
+                error: [
+                    '# :warning: **Performance Alert** :warning:',
+                    '',
+                    "Possible performance regression was detected for benchmark **'Test benchmark'**.",
+                    'Benchmark result of this commit is worse than the previous benchmark result exceeding threshold `2`.',
+                    '',
+                    '| Benchmark suite | Current: current commit id | Previous: prev commit id | Ratio |',
+                    '|-|-|-|-|',
+                    '| `bench_fib_10` | `20` ns/iter (`± 20`) | `100` ns/iter (`± 20`) | `5` |',
+                    '',
+                    `This comment was automatically generated by [workflow](${serverUrl}/user/repo/actions?query=workflow%3AWorkflow%20name) using [github-action-benchmark](https://github.com/marketplace/actions/continuous-benchmark).`,
+                    '',
+                    'CC: @user',
+                ],
+            },
             {
                 it: 'raises an alert with tool whose result value is bigger-is-better',
                 config: defaultCfg,