<html> <head> <title></title> <script type="text/javascript"> function upper(){ document.getElementById('field').value = document.getElementById('field').value.toUpperCase();// 1行で書いてください } function lower(){ document.getElementById('field').value = document.getElementById('field').value.toLowerCase();// 1行で書いてください } </script> </head> <body> <input type="text" id="field" maxlength="10"> <input type="button" value="大文字に変換" onclick="upper();"> <input type="button" value="小文字に変換" onclick="lower();"> </body> </html>