diff --git a/src/evaluator/builtin/index.ts b/src/evaluator/builtin/index.ts
index be4eba5..36c0c19 100644
--- a/src/evaluator/builtin/index.ts
+++ b/src/evaluator/builtin/index.ts
@@ -1,9 +1,9 @@
 import type * as Value from "../value";
 import * as value from "../value";
 
-export type BuiltinFunction = (args: any) => Value.Value;
+export type BuiltinFunction = (args: any[], onStdout?: (toWrite: string) => void) => Value.Value;
 
-const len: BuiltinFunction = (args: Value.Value[]) => {
+const len: BuiltinFunction = (args) => {
   const arg = args[0];
   if (arg.type === "string") {
     const length = arg.value.length;
@@ -13,11 +13,27 @@ const len: BuiltinFunction = (args: Value.Value[]) => {
   throw new Error();
 };
 
+const write: BuiltinFunction = (args, onStdout) => {
+  if (args.length === 0) {
+    throw new Error();
+  }
+
+  const str = args.map(arg => arg.representation).join(" ");
+  if (onStdout !== undefined) {
+    onStdout(str);
+  }
+
+  const range = { begin: args[0].range.begin, end: args[args.length-1].range.end };
+  return value.createEmptyValue({ value: null }, "(없음)", range);
+};
+
 const builtins = {
   get(identifier: string): BuiltinFunction | null {
     switch (identifier) {
       case "길이":
         return len;
+      case "쓰기":
+        return write;
       default:
         return null;
     }
diff --git a/src/evaluator/index.test.ts b/src/evaluator/index.test.ts
index 4e5eb22..2e8e497 100644
--- a/src/evaluator/index.test.ts
+++ b/src/evaluator/index.test.ts
@@ -3,12 +3,15 @@ import Parser from "../parser";
 import Evaluator, * as Eval from "./";
 import Environment from "./environment";
 
-const evaluateInput = (input: string) => {
+const evaluateInput = (input: string, onStdout?: (toWrite: string) => void) => {
   const lexer = new Lexer(input);
   const parser = new Parser(lexer);
   const parsed = parser.parseSource();
 
   const evaluator = new Evaluator();
+  if (onStdout !== undefined) {
+    evaluator.onStdout(onStdout);
+  }
   const env = new Environment();
   const evaluated = evaluator.evaluate(parsed, env);
   return evaluated;
@@ -35,6 +38,14 @@ const testEvaluatingFunction = ({ input, expectedParamsLength }: { input: string
   expect(evaluated).toHaveProperty("environment");
 };
 
+const testEvaluatingStdout = ({ input, expected }: { input: string, expected: any }): void => {
+  const stdouts: string[] = [];
+
+  evaluateInput(input, toWrite => stdouts.push(toWrite));
+
+  expect(stdouts).toEqual(expected);
+};
+
 describe("evaluate()", () => {
   describe("single numbers", () => {
     const cases = [
@@ -358,20 +369,44 @@ describe("evaluate()", () => {
   });
 
   describe("builtin function calls", () => {
-    const cases = [
-      {
-        name: "length function for empty string",
-        input: "길이('')",
-        expected: 0,
-      },
-      {
-        name: "length function for nonempty string",
-        input: "길이('사과')",
-        expected: 2,
-      },
-    ];
+    describe("길이()", () => {
+      const cases = [
+        {
+          name: "empty string",
+          input: "길이('')",
+          expected: 0,
+        },
+        {
+          name: "nonempty string",
+          input: "길이('사과')",
+          expected: 2,
+        },
+      ];
+
+      it.each(cases)("evaluate $name", testEvaluatingPrimitive);
+    });
 
-    it.each(cases)("evaluate $name", testEvaluatingPrimitive);
+    describe("쓰기()", () => {
+      const cases = [
+        {
+          name: "single string",
+          input: "쓰기('사과')",
+          expected: ["사과"],
+        },
+        {
+          name: "multiple string",
+          input: "쓰기('사과', '포도', '바나나')",
+          expected: ["사과 포도 바나나"],
+        },
+        {
+          name: "multiple calls",
+          input: "쓰기('사과') 쓰기('포도')",
+          expected: ["사과", "포도"],
+        },
+      ];
+
+      it.each(cases)("evaluate $name", testEvaluatingStdout);
+    });
   });
 
   describe("errors", () => {
diff --git a/src/evaluator/index.ts b/src/evaluator/index.ts
index d4e5425..89459b1 100644
--- a/src/evaluator/index.ts
+++ b/src/evaluator/index.ts
@@ -26,10 +26,16 @@ export class BadIdentifierError extends EvalError {};
 type ComparisonOperator = "==" | "!=" | ">" | "<" | ">=" | "<=";
 
 export default class Evaluator {
+  private callbackOnStdout?: (toWrite: string) => void;
+
   evaluate(node: Node.ProgramNode, env: Environment): Value.Value {
     return this.evaluateProgram(node, env);
   }
 
+  onStdout(callback: (toWrite: string) => void): void {
+    this.callbackOnStdout = callback;
+  }
+
   private evaluateProgram(node: Node.ProgramNode, env: Environment): Value.Value {
     const { statements } = node;
 
@@ -242,7 +248,8 @@ export default class Evaluator {
   }
 
   private evaluateBuiltinFunctionCall(func: Value.BuiltinFunctionValue, callArguments: Value.Value[]): Value.Value {
-    return func.body(callArguments);
+    const callbackOnStdout = this.callbackOnStdout === undefined ? undefined : this.callbackOnStdout.bind(this);
+    return func.body(callArguments, callbackOnStdout);
   }
 
   private getBooleanComparisonInfixOperationValue(left: boolean, right: boolean, operator: ComparisonOperator): boolean {
diff --git a/src/evaluator/value/index.ts b/src/evaluator/value/index.ts
index 9b7aa14..a72fded 100644
--- a/src/evaluator/value/index.ts
+++ b/src/evaluator/value/index.ts
@@ -35,7 +35,7 @@ export interface EmptyValue extends ValueBase<"empty"> {
   readonly value: null,
 }
 export interface BuiltinFunctionValue extends ValueBase<"builtin function"> {
-  readonly body: (args: any) => Value,
+  readonly body: (args: any, onStdout?: (toWrite: string) => void) => Value,
 }
 
 export interface ReturnValue {
diff --git a/src/index.test.ts b/src/index.test.ts
index 3eed534..26d817d 100644
--- a/src/index.test.ts
+++ b/src/index.test.ts
@@ -52,6 +52,15 @@ it("execute assignment and calculation", () => {
   expect(execute("변수1 = 4  변수2 = 9  ((변수1 - 변수2) * 변수1)")).toBe("-20");
 });
 
-it("execute builtin 길이 function", () => {
+it("execute builtin function 길이()", () => {
   expect(execute("길이('사과')")).toBe("2");
 });
+
+it("execute builtin function 쓰기()", () => {
+  const stdouts: string[] = [];
+  const onStdout = (toWrite: string) => stdouts.push(toWrite);
+
+  execute("쓰기('사과') 쓰기('포도', '바나나')", onStdout);
+
+  expect(stdouts).toEqual(["사과", "포도 바나나"]);
+});
diff --git a/src/index.ts b/src/index.ts
index c52c336..9a2a30d 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -2,12 +2,16 @@ import Lexer from "./lexer";
 import Parser from "./parser";
 import Evaluator, { Environment } from "./evaluator";
 
-export const execute = (input: string): string => {
+export const execute = (input: string, callbackOnStdout?: (toWrite: string) => void): string => {
   const lexer = new Lexer(input);
   const parser = new Parser(lexer);
   const parsed = parser.parseSource();
 
   const evaluator = new Evaluator();
+  if (callbackOnStdout !== undefined) {
+    evaluator.onStdout(callbackOnStdout);
+  }
+
   const environment = new Environment();
   const evaluated = evaluator.evaluate(parsed, environment);