function youbi() {
	var youbiflag=0;
	if(document.mail_form.oyear.value.match(/[^0-9]+/)){
		youbiflag = 1;
	}
	if(document.mail_form.omonth.value.match(/[^0-9]+/)){
		youbiflag = 1;
	}
	if(document.mail_form.oday.value.match(/[^0-9]+/)){
		youbiflag = 1;
	}
	if(document.mail_form.oyear.value<2008 || document.mail_form.oyear.value>2030){
		youbiflag = 2;
	}
	if(document.mail_form.omonth.value<1 || document.mail_form.omonth.value>12){
		youbiflag = 2;
	}
	if(document.mail_form.oday.value<1 || document.mail_form.oday.value>31){
		youbiflag = 2;
	}
	
	var di = new Date(document.mail_form.oyear.value,document.mail_form.omonth.value-1,document.mail_form.oday.value);
	if(di.getFullYear() == document.mail_form.oyear.value && di.getMonth() == document.mail_form.omonth.value-1 && di.getDate() == document.mail_form.oday.value){
	}else{
		youbiflag = 2;	
	}

	if(youbiflag==0){
	myWeekTbl = new Array( "日","月","火","水","木","金","土" );
	myDate = new Date(document.mail_form.oyear.value ,document.mail_form.omonth.value-1,document.mail_form.oday.value);
	myWeek = myDate.getDay();
	document.mail_form.oyoubi.value=myWeekTbl[myWeek] ;
	}else{
	document.mail_form.oyoubi.value="";
	}
}