function go(number){
	var now=(replay!=null?replay:tesuu);
	if(isNaN(number)) return false;
	if(number<now){
		goback(now-number);
	}else{
		goforward(number-now);
	}
	return true;
}

<td colspan="3" align="center">
					<button onclick="goback(replay!=null?replay:tesuu)"><<</button>
					<button onclick="goback(1)"><</button>
					<form onsubmit="go(this.tesuu.value);return false;" style="display:inline">
					   <input type="text" name="tesuu" size=3>
					</form>
					<button onclick="goforward(1)">></button>
					<button onclick="goforward(replay!=null?tesuu-replay:tesuu)">>></button>
				</td>