<script type="text/javascript"><!--
var doc_sctop,stop_point,moint;
function page_top(st){
stop_point=(!st)?0:st;
doc_sctop = document.body.scrollTop;
moint=doc_sctop-stop_point;
page_move();
}

function page_move(){
if(doc_sctop <= stop_point)return;
moint = moint*0.9;
scroll(0,moint+stop_point);
if(moint > 1)
   setTimeout("page_move()",3);
}/*himajin.moo.jp*/
// --></script>

<button onclick="page_top()">PAGE TOP</button>
<button onclick="page_top(300)">PAGE TOP300px</button>