menu_time = [
["40分","50分","70分"],
["40分","60分","70分","80分","100分","120分"],
["40分","60分","70分","80分","100分","120分"],
["40分","60分","80分"],
["120分","180分","240分"],
["100分"],
["40分","50分","70分"],
["80分","100分","120分"]
];


function setMenuItem(n){
  itemNum = menu_time[n].length;

  obj = document.myForm.プレイ時間.options;
  obj.length=0; 

　for (i=0; i<itemNum; i++){
　　document.myForm.プレイ時間.options[i] = new Option(menu_time[n][i],menu_time[n][i]);
　}
}