//(省略) private void ThisAddIn_Startup(object sender, System.EventArgs e) { this.Application.WorkbookActivate += Application_Active; this.Application.SheetActivate += Sheet_Active; } void Application_Active(Excel.Workbook wb) { //起動時の処理を書きます~ Excel.Worksheet activeWorksheet = ((Excel.Worksheet)Application.ActiveSheet); MessageBox.Show(activeWorksheet.Name, string.Empty, MessageBoxButtons.OK, Messag