document.write("<p>経過時間：<input type=\"text\" name=\"chktm\" id=\"chktm\" size=\"8\" value=\"00:00:00\" style=\"font-size:300%;\" /></p>");
hour=0; min=0; sec=0;
function count() {
 sec++;
   if(sec == 60) { min++; sec=0;
     if(min==60) { hour++; min=0; } }
 h = hour; m = min; s = sec;
 if(h<10) { h="0"+h;} if(m<10) {m="0"+m;} if(s<10){s="0"+s;}
document.getElementById('chktm').value = h+":"+m+":"+s;
}
var pastimer = setInterval('count()',1000);
window.onload = pastimer;