diff --git a/.gitignore b/.gitignore
index 3b1d510..1591736 100644
--- a/.gitignore
+++ b/.gitignore
@@ -29,11 +29,8 @@ go.work.sum
 # env file
 .env
 
-# Editor/IDE
-# .idea/
-# .vscode/
-
 # Editor/IDE
 .claude/
 
 test/
+.DS_Store
diff --git a/.issues/.counter b/.issues/.counter
index aabe6ec..2bd5a0a 100644
--- a/.issues/.counter
+++ b/.issues/.counter
@@ -1 +1 @@
-21
+22
diff --git a/.issues/closed/021-add-open-file-command-to-open-issue-markdown-in-de.md b/.issues/closed/021-add-open-file-command-to-open-issue-markdown-in-de.md
new file mode 100644
index 0000000..1213ce3
--- /dev/null
+++ b/.issues/closed/021-add-open-file-command-to-open-issue-markdown-in-de.md
@@ -0,0 +1,33 @@
+---
+id: "021"
+assignee: ""
+labels:
+    - feature
+created: 2026-02-06T14:27:24.912527+09:00
+updated: 2026-02-06T14:40:03.891202+09:00
+---
+
+# Add view command to open issue markdown in default program
+
+## Description
+
+Add a new `gi view` command that opens an issue's markdown file using the system's default program associated with the `.md` extension. This allows users to quickly view or edit issues in their preferred markdown editor or viewer (e.g., Typora, VS Code, Obsidian).
+
+Usage: `gi view 001`
+
+## Requirements
+
+- Accept an issue ID as argument (e.g., `gi view 001`)
+- Look up the issue file in `.issues/open/` and `.issues/closed/`
+- Open the file using the OS default program for `.md` files:
+  - macOS: use `open` command
+  - Linux: use `xdg-open` command
+- Show an error if the issue ID is not found
+
+## Success Criteria
+
+- [ ] `gi view <id>` opens the issue markdown in the default associated program
+- [ ] Works on macOS (`open`) and Linux (`xdg-open`)
+- [ ] Displays clear error when issue ID does not exist
+- [ ] Unit tests for file lookup logic
+- [ ] Update README file
diff --git a/README.md b/README.md
index 777c842..472187e 100644
--- a/README.md
+++ b/README.md
@@ -82,6 +82,13 @@ gi edit 001
 # Opens the issue file in $EDITOR (defaults to vim)
 ```
 
+### View an issue in default program
+
+```bash
+gi view 001
+# Opens the issue markdown file in the system's default program
+```
+
 ### Search issues
 
 ```bash
diff --git a/cmd/view.go b/cmd/view.go
new file mode 100644
index 0000000..0ebc6fd
--- /dev/null
+++ b/cmd/view.go
@@ -0,0 +1,52 @@
+package cmd
+
+import (
+	"fmt"
+	"os/exec"
+	"runtime"
+
+	"github.com/Allra-Fintech/git-issue/pkg"
+	"github.com/fatih/color"
+	"github.com/spf13/cobra"
+)
+
+var viewCmd = &cobra.Command{
+	Use:   "view <issue-id>",
+	Short: "Open an issue in the default program",
+	Long:  `Open an issue's markdown file in the system's default program (e.g., Typora, VS Code, Obsidian).`,
+	Args:  cobra.ExactArgs(1),
+	RunE:  runView,
+}
+
+func init() {
+	rootCmd.AddCommand(viewCmd)
+}
+
+func runView(cmd *cobra.Command, args []string) error {
+	issueID := args[0]
+
+	// Find the issue file
+	path, _, err := pkg.FindIssueFile(issueID)
+	if err != nil {
+		return fmt.Errorf("failed to find issue: %w", err)
+	}
+
+	// Determine the OS-appropriate open command
+	var opener string
+	switch runtime.GOOS {
+	case "darwin":
+		opener = "open"
+	case "linux":
+		opener = "xdg-open"
+	default:
+		return fmt.Errorf("unsupported platform: %s", runtime.GOOS)
+	}
+
+	// Open the file in the default program (non-blocking)
+	if err := exec.Command(opener, path).Start(); err != nil {
+		return fmt.Errorf("failed to open file: %w", err)
+	}
+
+	color.New(color.FgGreen).Printf("✓ Opened issue #%s in default program\n", issueID)
+	return nil
+}
diff --git a/cmd/view_test.go b/cmd/view_test.go
new file mode 100644
index 0000000..7e25e51
--- /dev/null
+++ b/cmd/view_test.go
@@ -0,0 +1,21 @@
+package cmd
+
+import (
+	"testing"
+)
+
+func TestViewMissingArgs(t *testing.T) {
+	cmd := viewCmd
+	err := cmd.Args(cmd, []string{})
+	if err == nil {
+		t.Error("expected error for missing arguments")
+	}
+}
+
+func TestViewNonExistentIssue(t *testing.T) {
+	// runView should fail when the issue doesn't exist
+	err := runView(viewCmd, []string{"999"})
+	if err == nil {
+		t.Error("expected error for non-existent issue")
+	}
+}