<select id="myselect1"> <option value="">― ―</option> <option value="2015級">2015級</option> <option value="2014級">2014級</option> <option value="2013級">2013級</option> <option value="2012級">2012級</option></select><br><br><select id="myselect2"> <option value="">― ―</option> <option value="2015級">2015級</option> <option value="2014級">2014級</option> <option value="2013級">2013級</option> <option value="2012級">2012級</option></select> var time = new Date(); var month=time.getMonth()+1; var day=time.getDay(); if(month>5&&day>1){  var objSelect=document.getElementById("myselect2");  objSelect.options.add(new Option("2016級", "2016級"),1);  objSelect.options.remove(5); } if(month>7&&day>1){  var objSelect=document.getElementById("myselect1");  objSelect.options.add(new Option("2016級", "2016級"),1);  objSelect.options.remove(5); }