diff --git a/MainForm.cs b/MainForm.cs
index d2dddfc..a211982 100644
--- a/MainForm.cs
+++ b/MainForm.cs
@@ -21,6 +21,8 @@
         private readonly Timer _uiTimer;
 
         private TabControl _tabs;
+        private TabPage _apertureTabPage;
+        private TabPage _focusTabPage;
         private PictureBox _focusPicture;
         private Label _focusCurrentValue;
         private Label _focusMaxValue;
@@ -82,14 +84,14 @@
             };
             _tabs.DrawItem += Tabs_DrawItem;
 
-            TabPage focusPage = new TabPage("フォーカス調整");
-            TabPage aperturePage = new TabPage("開口調整");
+            _focusTabPage = new TabPage("フォーカス調整");
+            _apertureTabPage = new TabPage("開口調整");
 
-            BuildFocusPage(focusPage);
-            BuildAperturePage(aperturePage);
+            BuildFocusPage(_focusTabPage);
+            BuildAperturePage(_apertureTabPage);
 
-            _tabs.TabPages.Add(focusPage);
-            _tabs.TabPages.Add(aperturePage);
+            _tabs.TabPages.Add(_apertureTabPage);
+            _tabs.TabPages.Add(_focusTabPage);
             _tabs.SelectedIndex = 0;
 
             var statusStrip = new StatusStrip();
@@ -429,7 +431,7 @@
                 //Text = "フォーカス調整 \u2014 Lens Adjustment Tool";
                 _logger.Info("Application start.");
                 RestoreApertureRoi();
-                _processor.SetMode(AdjustmentMode.Focus, resetFocusMaximum: true);
+                ApplySelectedMode(clearMailbox: false);
                 _camera.InitializeAndStart(AppDomain.CurrentDomain.BaseDirectory);
                 _cameraInfoLabel.Text = _camera.CameraInfo?.ToString() ?? string.Empty;
                 _uiTimer.Start();
@@ -450,12 +452,18 @@
 
         private void Tabs_SelectedIndexChanged(object sender, EventArgs e)
         {
-            AdjustmentMode mode = _tabs.SelectedIndex == 0
-                ? AdjustmentMode.Focus
-                : AdjustmentMode.Aperture;
+            ApplySelectedMode(clearMailbox: true);
+        }
+
+        private void ApplySelectedMode(bool clearMailbox)
+        {
+            AdjustmentMode mode = GetSelectedMode();
 
             _processor.SetMode(mode, resetFocusMaximum: mode == AdjustmentMode.Focus);
-            _mailbox.Clear();
+            if (clearMailbox)
+            {
+                _mailbox.Clear();
+            }
 
             if (mode == AdjustmentMode.Focus)
             {
@@ -466,6 +474,13 @@
             _logger.Info("Mode changed: " + mode);
         }
 
+        private AdjustmentMode GetSelectedMode()
+        {
+            return _tabs.SelectedTab == _focusTabPage
+                ? AdjustmentMode.Focus
+                : AdjustmentMode.Aperture;
+        }
+
         private void FocusResetButton_Click(object sender, EventArgs e)
         {
             _processor.ResetFocusMaximum();