diff --git a/go/study/ch04_json/go.mod b/go/study/ch04_json/go.mod
new file mode 100644
index 00000000..198c7459
--- /dev/null
+++ b/go/study/ch04_json/go.mod
@@ -0,0 +1,3 @@
+module github.com/tecyokomichi/WebAppLearning/go/study/ch04_json
+
+go 1.19
diff --git a/go/study/ch04_json/main.go b/go/study/ch04_json/main.go
new file mode 100644
index 00000000..b4dc7b93
--- /dev/null
+++ b/go/study/ch04_json/main.go
@@ -0,0 +1,82 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+)
+
+type Person struct {
+	FirstName   string  `json:"first_name"`
+	LastName    string  `json:"last_name"`
+	Birthday    string  `json:"birthday"`
+	Age	    int     `json:"age"`
+}
+
+func main() {
+	if len(os.Args) < 2 {
+		showHelp()
+		os.Exit(1)
+	}
+	switch os.Args[1] {
+	case "example":
+		people := []*Person {
+			{
+				FirstName: "Blake",
+				LastName: "Serild",
+				Birthday: "1989-07-10",
+				Age: 33,
+			},
+			{
+				FirstName: "Libbie",
+				LastName: "Drisko",
+				Birthday: "1988-06-15",
+				Age: 24,
+			},
+			{
+				FirstName: "Anestassia",
+				LastName: "Truc",
+				Birthday: "1973-04-02",
+				Age: 48,
+			},
+		}
+
+		b, err := json.MarshalIndent(people, "", "\t")
+		if err != nil {
+			fmt.Printf("Error: %v", err)
+			os.Exit(1)
+		}
+		fmt.Println(string(b))
+	case "summary":
+		var people []*Person
+		if len(os.Args) < 3 || len(os.Args) > 3 {
+			showHelp()
+			os.Exit(1)
+		}
+		f, err := os.ReadFile(os.Args[2])
+		if err != nil {
+			fmt.Printf("Error: %v", err)
+			os.Exit(1)
+		}
+		err = json.Unmarshal(f, &people)
+		if err != nil {
+			fmt.Printf("Error: %v", err)
+			os.Exit(1)
+		}
+		count, sum := 0, 0
+		for _, p := range people {
+			count++
+			sum += p.Age
+		}
+		fmt.Printf("%d 人、平均年齢 %d \n", count, sum/count)
+	default:
+		showHelp()
+		os.Exit(1)
+	}
+}
+
+func showHelp() {
+	fmt.Printf("Usage:\n")
+	fmt.Printf("%s example\n", os.Args[0])
+	fmt.Printf("Shows an example of JSON data\n")
+}
\ No newline at end of file
diff --git a/go/study/ch04_json/people.json b/go/study/ch04_json/people.json
new file mode 100644
index 00000000..f46a81d4
--- /dev/null
+++ b/go/study/ch04_json/people.json
@@ -0,0 +1,32 @@
+[
+  {
+    "first_name": "Blake",
+    "last_name": "Serilda",
+    "birthday": "1989-07-10",
+    "age": 33
+  },
+  {
+    "first_name": "Libbie",
+    "last_name": "Drisko",
+    "birthday": "1998-06-15",
+    "age": 24
+  },
+  {
+    "first_name": "Anestassia",
+    "last_name": "Truc",
+    "birthday": "1973-04-02",
+    "age": 48
+  },
+  {
+    "first_name": "Cyndie",
+    "last_name": "Syd",
+    "birthday": "1985-07-12",
+    "age": 37
+  },
+  {
+    "first_name": "Joelly",
+    "last_name": "Honoria",
+    "birthday": "2012-01-31",
+    "age": 10
+  }
+]