diff --git a/src/main.ts b/src/main.ts
index 373c161c..bc6c4a33 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -1,4 +1,4 @@
-import * as core from "@actions/core";
+import { debug, warning, getInput, setFailed } from "@actions/core";
 import { context } from "@actions/github";
 import { WebhookPayload } from "@actions/github/lib/interfaces";
 
@@ -35,13 +35,13 @@ export const convertToSlackUsername = (
   githubUsernames: string[],
   mapping: MappingFile
 ): string[] => {
-  core.debug(JSON.stringify({ githubUsernames }, null, 2));
+  debug(JSON.stringify({ githubUsernames }, null, 2));
 
   const slackIds = githubUsernames
     .map((githubUsername) => mapping[githubUsername])
     .filter((slackId) => slackId !== undefined) as string[];
 
-  core.debug(JSON.stringify({ slackIds }, null, 2));
+  debug(JSON.stringify({ slackIds }, null, 2));
 
   return slackIds;
 };
@@ -80,7 +80,7 @@ export const execPrReviewRequestedMention = async (
   );
 
   if (slackUserIds.length === 0 && slackUserGroupIds.length === 0) {
-    core.debug(
+    debug(
       "finish execPrReviewRequestedMention because slackUserIds and slackUserGroupIds length === 0"
     );
     return;
@@ -107,13 +107,13 @@ export const execNormalMention = async (
   const info = pickupInfoFromGithubPayload(payload);
 
   if (info.body === null) {
-    core.debug("finish execNormalMention because info.body === null");
+    debug("finish execNormalMention because info.body === null");
     return;
   }
 
   const githubUsernames = pickupUsername(info.body);
   if (githubUsernames.length === 0) {
-    core.debug("finish execNormalMention because githubUsernames.length === 0");
+    debug("finish execNormalMention because githubUsernames.length === 0");
     return;
   }
 
@@ -121,7 +121,7 @@ export const execNormalMention = async (
   const slackIdsWithoutIgnore = arrayDiff(slackIds, ignoreSlackIds);
 
   if (slackIdsWithoutIgnore.length === 0) {
-    core.debug("finish execNormalMention because slackIds.length === 0");
+    debug("finish execNormalMention because slackIds.length === 0");
     return;
   }
 
@@ -140,9 +140,7 @@ export const execNormalMention = async (
     botName,
   });
 
-  core.debug(
-    ["postToSlack result", JSON.stringify({ result }, null, 2)].join("\n")
-  );
+  debug(["postToSlack result", JSON.stringify({ result }, null, 2)].join("\n"));
 };
 
 export const execApproveMention = async (
@@ -164,7 +162,7 @@ export const execApproveMention = async (
   const slackIds = convertToSlackUsername([prOwnerGithubUsername], mapping);
 
   if (slackIds.length === 0) {
-    core.debug("finish execApproveMention because slackIds.length === 0");
+    debug("finish execApproveMention because slackIds.length === 0");
     return null;
   }
 
@@ -188,7 +186,7 @@ export const execApproveMention = async (
     { iconUrl, botName }
   );
 
-  core.debug(
+  debug(
     ["postToSlack result", JSON.stringify({ postSlackResult }, null, 2)].join(
       "\n"
     )
@@ -211,7 +209,7 @@ export const execPostError = async (
   const currentJobUrl = runId ? buildCurrentJobUrl(runId) : undefined;
   const message = buildSlackErrorMessage(error, currentJobUrl);
 
-  core.warning(message);
+  warning(message);
 
   const { slackWebhookUrl, iconUrl, botName } = allInputs;
 
@@ -219,25 +217,25 @@ export const execPostError = async (
 };
 
 const getAllInputs = (): AllInputs => {
-  const slackWebhookUrl = core.getInput("slack-webhook-url", {
+  const slackWebhookUrl = getInput("slack-webhook-url", {
     required: true,
   });
 
   if (!slackWebhookUrl) {
-    core.setFailed("Error! Need to set `slack-webhook-url`.");
+    setFailed("Error! Need to set `slack-webhook-url`.");
   }
 
-  const repoToken = core.getInput("repo-token", { required: true });
+  const repoToken = getInput("repo-token", { required: true });
   if (!repoToken) {
-    core.setFailed("Error! Need to set `repo-token`.");
+    setFailed("Error! Need to set `repo-token`.");
   }
 
-  const iconUrl = core.getInput("icon-url", { required: false });
-  const botName = core.getInput("bot-name", { required: false });
-  const configurationPath = core.getInput("configuration-path", {
+  const iconUrl = getInput("icon-url", { required: false });
+  const botName = getInput("bot-name", { required: false });
+  const configurationPath = getInput("configuration-path", {
     required: true,
   });
-  const runId = core.getInput("run-id", { required: false });
+  const runId = getInput("run-id", { required: false });
 
   return {
     repoToken,
@@ -250,13 +248,13 @@ const getAllInputs = (): AllInputs => {
 };
 
 export const main = async (): Promise<void> => {
-  core.debug("start main()");
+  debug("start main()");
 
   const { payload } = context;
-  core.debug(JSON.stringify({ payload }, null, 2));
+  debug(JSON.stringify({ payload }, null, 2));
 
   const allInputs = getAllInputs();
-  core.debug(JSON.stringify({ allInputs }, null, 2));
+  debug(JSON.stringify({ allInputs }, null, 2));
 
   const { repoToken, configurationPath } = allInputs;
 
@@ -275,7 +273,7 @@ export const main = async (): Promise<void> => {
       );
     })();
 
-    core.debug(JSON.stringify({ mapping }, null, 2));
+    debug(JSON.stringify({ mapping }, null, 2));
 
     if (payload.action === "review_requested") {
       await execPrReviewRequestedMention(
@@ -284,7 +282,7 @@ export const main = async (): Promise<void> => {
         mapping,
         SlackRepositoryImpl
       );
-      core.debug("finish execPrReviewRequestedMention()");
+      debug("finish execPrReviewRequestedMention()");
       return;
     }
 
@@ -302,7 +300,7 @@ export const main = async (): Promise<void> => {
         ignoreSlackIds.push(sentSlackUserId);
       }
 
-      core.debug(
+      debug(
         [
           "execApproveMention()",
           JSON.stringify({ sentSlackUserId }, null, 2),
@@ -317,9 +315,9 @@ export const main = async (): Promise<void> => {
       SlackRepositoryImpl,
       ignoreSlackIds
     );
-    core.debug("finish execNormalMention()");
+    debug("finish execNormalMention()");
   } catch (error: unknown) {
     await execPostError(error as Error, allInputs, SlackRepositoryImpl);
-    core.warning(JSON.stringify({ payload }, null, 2));
+    warning(JSON.stringify({ payload }, null, 2));
   }
 };