diff --git a/go/study/ch02_first_cli_app/calc.go b/go/study/ch02_first_cli_app/calc.go
new file mode 100644
index 00000000..a0594804
--- /dev/null
+++ b/go/study/ch02_first_cli_app/calc.go
@@ -0,0 +1,80 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+)
+
+type Calculation interface {
+	Do(x, y int) Result
+	Kind() string
+}
+
+type Result interface {
+	Outcome() string
+}
+
+type Int int
+
+func (i Int) Outcome() string {
+	return strconv.Itoa(int(i))
+}
+
+type Addition struct{}
+
+func (*Addition) Kind() string {
+	return "addition"	
+}
+
+func (*Addition) Do(x, y int) Result {
+	return Int(x + y)
+}
+
+type Subtraction struct{}
+
+func (*Subtraction) Kind() string {
+	return "subtraction"	
+}
+
+func (*Subtraction) Do(x, y int) Result {
+	return Int(x - y)
+}
+
+type Multiplication struct{}
+
+func (*Multiplication) Kind() string {
+	return "multiplication"
+}
+
+func (*Multiplication) Do(x, y int) Result {
+	return Int(x * y)
+}
+
+type DivisionResult struct {
+	Quotient int
+	Remainder int
+}
+
+func (d *DivisionResult) Outcome() string {
+	return fmt.Sprintf("(quotient: %d, remainder: %d)", d.Quotient, d.Remainder)
+}
+
+type InvalidDenominator struct{}
+
+func (i *InvalidDenominator) Outcome() string {
+	return "Invalid denominator. It must be not zero"
+}
+
+type Division struct{}
+
+func (d *Division) Kind() string {
+	return "division"
+}
+
+func (d *Division) Do(x, y int) Result {
+	if y == 0 {
+		return &InvalidDenominator{}
+	}
+	q, r := x/y, x%y
+	return &DivisionResult{q, r}
+}
diff --git a/go/study/ch02_first_cli_app/calc_test.go b/go/study/ch02_first_cli_app/calc_test.go
new file mode 100644
index 00000000..5d22ad99
--- /dev/null
+++ b/go/study/ch02_first_cli_app/calc_test.go
@@ -0,0 +1,48 @@
+package main
+
+import "testing"
+
+func TestAddtion(t *testing.T) {
+	calc := &Addition{}
+	if calc.Kind() != "addition" {
+		t.FailNow()
+	}
+	if calc.Do(1, 2) != Int(3) {
+		t.FailNow()
+	}
+}
+
+func TestSubtraction(t *testing.T) {
+	calc := &Subtraction{}
+	if calc.Kind() != "subtraction" {
+		t.FailNow()
+	}
+	if calc.Do(2, 1) != Int(1) {
+		t.FailNow()
+	}
+}
+
+func TestMultiplication(t *testing.T) {
+	calc := &Multiplication{}
+	if calc.Kind() != "multiplication" {
+		t.FailNow()
+	}
+	if calc.Do(2, 3) != Int(6) {
+		t.FailNow()
+	}
+}
+
+func TestDivision(t *testing.T) {
+	calc := &Division{}
+	if calc.Kind() != "division" {
+		t.FailNow()
+	}
+	if _, ok := calc.Do(2, 0).(*InvalidDenominator); !ok {
+		t.FailNow()
+	}
+	if r, ok := calc.Do(10, 3).(*DivisionResult); ok {
+		if r.Quotient != 3 || r.Remainder != 1 {
+			t.FailNow()
+		}
+	}
+}
diff --git a/go/study/ch02_first_cli_app/go.mod b/go/study/ch02_first_cli_app/go.mod
new file mode 100644
index 00000000..b8982bd0
--- /dev/null
+++ b/go/study/ch02_first_cli_app/go.mod
@@ -0,0 +1,3 @@
+module github.com/tecyokomichi/WebAppLearning/go/study/ch02_first_cli_app
+
+go 1.19
diff --git a/go/study/ch02_first_cli_app/main.go b/go/study/ch02_first_cli_app/main.go
new file mode 100644
index 00000000..d934c9cc
--- /dev/null
+++ b/go/study/ch02_first_cli_app/main.go
@@ -0,0 +1,54 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"strconv"
+)
+
+var calcMap = map[string]Calculation{
+	"add":			&Addition{},
+	"subtract":		&Subtraction{},
+	"multiply":		&Multiplication{},
+	"divide":		&Division{},
+}
+
+func main() {
+	if len(os.Args) < 4 || 4 < len(os.Args) {
+		showHelp()
+		os.Exit(1)
+	} else if len(os.Args) == 4 {
+		calc, ok := calcMap[os.Args[1]]
+		if !ok {
+			showHelp()
+			os.Exit(1)
+		}
+		x, e := parseInt(os.Args[2])
+		if  e != nil {
+			fmt.Printf("%s\n", e.Error())
+			os.Exit(1)
+		}
+		y, e := parseInt(os.Args[3])
+		if  e != nil {
+			fmt.Printf("%s\n", e.Error())
+			os.Exit(1)
+		}
+		fmt.Printf("%s: %s\n", calc.Kind(), calc.Do(x, y).Outcome())
+		os.Exit(0)
+	}
+}
+
+func showHelp() {
+	fmt.Println("USAGE:")
+	fmt.Println("./ch02_first_cli (add|subtract|multiply|divide) X Y")
+	fmt.Println(" Shows the result of calculation with X and Y")
+	fmt.Println(" X and Y must be number")
+}
+
+func parseInt(s string) (int, error) {
+	r, err := strconv.Atoi(s)
+	if err != nil {
+		return 0, fmt.Errorf("ERROR: %q is not a number", s)
+	}
+	return r, nil
+}