diff --git a/README.md b/README.md
index 16dcac0..2669829 100644
--- a/README.md
+++ b/README.md
@@ -4,9 +4,22 @@ Export GitHub Actions secrets as environment variables.
 
 ## Usage
 
-```yml
+Set the JSON of secrets to `secrets`.
+
+```yaml
+steps:
+  - uses: koyashiro/export-secrets-action@v0.1.0
+    with:
+      secrets: ${{ toJSON(secrets) }}
+```
+
+If you want to downcase secrets starting with `TF_VAR_`, you can use the `downcase-tf-var` option.
+For example, a secret like `TF_VAR_EXAMPLE` will be exported as `TF_VAR_example`.
+
+```yaml
 steps:
   - uses: koyashiro/export-secrets-action@v0.1.0
     with:
       secrets: ${{ toJSON(secrets) }}
+      downcase-tf-var: true
 ```
diff --git a/action.yml b/action.yml
index a9d69be..c29164d 100644
--- a/action.yml
+++ b/action.yml
@@ -5,6 +5,9 @@ inputs:
   secrets:
     description: JSON representation of secrets
     required: true
+  downcase-tf-var:
+    description: Set this option if you want to downcase the secrets starting with `TF_VAR_`
+    required: false
 runs:
   using: node20
   main: dist/index.js
diff --git a/dist/index.js b/dist/index.js
index 01bc7f1..30c15b3 100644
--- a/dist/index.js
+++ b/dist/index.js
@@ -30847,11 +30847,15 @@ var z = /*#__PURE__*/Object.freeze({
 const secretsSchema = z.record(z.string(), z.string());
 function exportSecrets(core) {
     const secretsJson = core.getInput("secrets");
+    const downcaseTfVar = core.getInput("downcase-tf-var") === "true";
     if (!secretsJson) {
         throw new Error("secrets is required");
     }
     const secrets = secretsSchema.parse(JSON.parse(secretsJson));
     for (const [key, value] of Object.entries(secrets)) {
+        if (downcaseTfVar && key.startsWith("TF_VAR_")) {
+            core.exportVariable(`TF_VAR_${key.replace(/^TF_VAR_/, "").toLowerCase()}`, value);
+        }
         core.exportVariable(key, value);
     }
 }
diff --git a/src/lib.test.ts b/src/lib.test.ts
index f5b813c..4291acf 100644
--- a/src/lib.test.ts
+++ b/src/lib.test.ts
@@ -5,11 +5,16 @@ import { exportSecrets } from "./lib";
 describe("exportSecrets()", () => {
   describe("success", () => {
     const coreMock = {
-      getInput: vi
-        .fn()
-        .mockReturnValue(
-          '{"KEY_A":"VALUE_A","KEY_B":"VALUE_B","KEY_C":"VALUE_C"}',
-        ),
+      getInput: vi.fn().mockImplementation((s: string) => {
+        switch (s) {
+          case "secrets":
+            return '{"KEY_A":"VALUE_A","KEY_B":"VALUE_B","KEY_C":"VALUE_C","TF_VAR_KEY_D":"VALUE_D"}';
+          case "downcase-tf-var":
+            return "";
+          default:
+            return "";
+        }
+      }),
       exportVariable: vi.fn(),
     };
 
@@ -23,7 +28,64 @@ describe("exportSecrets()", () => {
       expect(coreMock.getInput).toHaveBeenCalledWith("secrets");
     });
 
-    it("calls exportVariable() 3 times", () => {
+    it('calls getInput() with "downcase-tf-var"', () => {
+      expect(coreMock.getInput).toHaveBeenCalledWith("downcase-tf-var");
+    });
+
+    it("calls exportVariable() 4 times", () => {
+      expect(coreMock.exportVariable).toHaveBeenNthCalledWith(
+        1,
+        "KEY_A",
+        "VALUE_A",
+      );
+      expect(coreMock.exportVariable).toHaveBeenNthCalledWith(
+        2,
+        "KEY_B",
+        "VALUE_B",
+      );
+      expect(coreMock.exportVariable).toHaveBeenNthCalledWith(
+        3,
+        "KEY_C",
+        "VALUE_C",
+      );
+      expect(coreMock.exportVariable).toHaveBeenNthCalledWith(
+        4,
+        "TF_VAR_KEY_D",
+        "VALUE_D",
+      );
+    });
+  });
+
+  describe("success_downcase-tf-var", () => {
+    const coreMock = {
+      getInput: vi.fn().mockImplementation((s: string) => {
+        switch (s) {
+          case "secrets":
+            return '{"KEY_A":"VALUE_A","KEY_B":"VALUE_B","KEY_C":"VALUE_C","TF_VAR_KEY_D":"VALUE_D"}';
+          case "downcase-tf-var":
+            return "true";
+          default:
+            return "";
+        }
+      }),
+      exportVariable: vi.fn(),
+    };
+
+    it("does not throws an error", () => {
+      expect(() => {
+        exportSecrets(coreMock as unknown as typeof core);
+      }).not.toThrow();
+    });
+
+    it('calls getInput() with "secrets"', () => {
+      expect(coreMock.getInput).toHaveBeenCalledWith("secrets");
+    });
+
+    it('calls getInput() with "downcase-tf-var"', () => {
+      expect(coreMock.getInput).toHaveBeenCalledWith("downcase-tf-var");
+    });
+
+    it("calls exportVariable() 4 times", () => {
       expect(coreMock.exportVariable).toHaveBeenNthCalledWith(
         1,
         "KEY_A",
@@ -39,12 +101,26 @@ describe("exportSecrets()", () => {
         "KEY_C",
         "VALUE_C",
       );
+      expect(coreMock.exportVariable).toHaveBeenNthCalledWith(
+        4,
+        "TF_VAR_key_d",
+        "VALUE_D",
+      );
     });
   });
 
   describe("secrets is empty", () => {
     const coreMock = {
-      getInput: vi.fn().mockReturnValue(""),
+      getInput: vi.fn().mockImplementation((s: string) => {
+        switch (s) {
+          case "secrets":
+            return "{";
+          case "downcase-tf-var":
+            return "";
+          default:
+            return "";
+        }
+      }),
       exportVariable: vi.fn(),
     };
 
@@ -58,6 +134,10 @@ describe("exportSecrets()", () => {
       expect(coreMock.getInput).toHaveBeenCalledWith("secrets");
     });
 
+    it('calls getInput() with "downcase-tf-var"', () => {
+      expect(coreMock.getInput).toHaveBeenCalledWith("downcase-tf-var");
+    });
+
     it("does not calls exportVariable()", () => {
       expect(coreMock.exportVariable).not.toHaveBeenCalled();
     });
@@ -65,7 +145,16 @@ describe("exportSecrets()", () => {
 
   describe("secret is invalid JSON", () => {
     const coreMock = {
-      getInput: vi.fn().mockReturnValue("{"),
+      getInput: vi.fn().mockImplementation((s: string) => {
+        switch (s) {
+          case "secrets":
+            return "{";
+          case "downcase-tf-var":
+            return "";
+          default:
+            return "";
+        }
+      }),
       exportVariable: vi.fn(),
     };
 
@@ -79,6 +168,10 @@ describe("exportSecrets()", () => {
       expect(coreMock.getInput).toHaveBeenCalledWith("secrets");
     });
 
+    it('calls getInput() with "downcase-tf-var"', () => {
+      expect(coreMock.getInput).toHaveBeenCalledWith("downcase-tf-var");
+    });
+
     it("does not calls exportVariable()", () => {
       expect(coreMock.exportVariable).not.toHaveBeenCalled();
     });
diff --git a/src/lib.ts b/src/lib.ts
index 8eb4997..719d934 100644
--- a/src/lib.ts
+++ b/src/lib.ts
@@ -7,6 +7,7 @@ const secretsSchema = z.record(z.string(), z.string());
 
 export function exportSecrets(core: ActionsCore) {
   const secretsJson = core.getInput("secrets");
+  const downcaseTfVar = core.getInput("downcase-tf-var") === "true";
 
   if (!secretsJson) {
     throw new Error("secrets is required");
@@ -15,6 +16,12 @@ export function exportSecrets(core: ActionsCore) {
   const secrets = secretsSchema.parse(JSON.parse(secretsJson));
 
   for (const [key, value] of Object.entries(secrets)) {
+    if (downcaseTfVar && key.startsWith("TF_VAR_")) {
+      core.exportVariable(
+        `TF_VAR_${key.replace(/^TF_VAR_/, "").toLowerCase()}`,
+        value,
+      );
+    }
     core.exportVariable(key, value);
   }
 }