function repositionObject()
{
  var top
    = eval(document.getElementById('float_img').style.top.replace('px', ''));
  var scrollTop
    = (this.document.body.scrollTop || this.document.documentElement.scrollTop);
  var d;
  if (top > scrollTop) {
    if (top - scrollTop > 1024) {
      d = 512;
    } else if (top - scrollTop > 512) {
      d = 256;
    } else if (top - scrollTop > 256) {
      d = 128;
    } else if (top - scrollTop > 128) {
      d = 64;
    } else if (top - scrollTop > 64) {
      d = 32;
    } else if (top - scrollTop > 32) {
      d = 16;
    } else if (top - scrollTop > 16) {
      d = 8;
    } else {
      if (top - scrollTop < 4) {
        d = top - scrollTop;
      } else {
        d = 4;
      }
    }
    
	var movePos = (top - d);
	//はじめの初期位置　topPos→htmlにも同じ値を
	var topPos = 150;
	if(movePos < topPos){
	 movePos = topPos;
	}
	
	
	document.getElementById('float_img').style.top = movePos + 'px';
    setTimeout('repositionObject()', 100);
  } else if (top < scrollTop) {
    if (scrollTop - top > 1024) {
      d = 512;
    } else if (scrollTop - top > 512) {
      d = 256;
    } else if (scrollTop - top > 256) {
      d = 128;
    } else if (scrollTop - top > 128) {
      d = 64;
    } else if (scrollTop - top > 64) {
      d = 32;
    } else if (scrollTop - top > 32) {
      d = 16;
    } else if (scrollTop - top > 16) {
      d = 8;
    } else {
      if (scrollTop - top < 4) {
        d = scrollTop - top;
      } else {
        d = 4;
      }
    }
    document.getElementById('float_img').style.top = (top + d) + 'px';
    setTimeout('repositionObject()', 100);
  }
}