function SmoothScroll(targetID){
  if( !document.getElementById ) {return true;}
  var step=10;  //初速度
  var max=400;  //最高速度
  var accel=4;  //加速度
  var interval=30;  //加速インターバル
  var current_y = document.body.scrollTop  || document.documentElement.scrollTop;
  var element=document.getElementById(targetID);
  if (!element){return true;}
  var target_y = 0;
  for (i = element;i.offsetParent;i=i.offsetParent ){
    target_y += i.offsetTop;
  }
  var count=0;
  if ( current_y > target_y ){ step = -(step); accel = -(accel);}
  var timerid = setInterval( function(){
    if (step<max) step += (count*accel);
    if ( Math.abs(current_y-target_y) < Math.abs(step) ){
      window.scrollTo((document.body.scrollTop  || document.documentElement.scrollTop),target_y);
      clearInterval(timerid);
      return false;
    }else{
      window.scrollBy(0,step);
      current_y += step;
      count++;
    }
  },interval);
  return false;
}