div实现多个UL标签滚动（ul内是4个li,里面是图片）

请问，怎么在800px,内的div实现点击左右按钮让ul的图片滚动，1次滚动1组ul

div_move_ul

<!-- Date: 2015-04-21 -->

<style type="text/css">
    .show_screen {width: 200px;height: 200px;overflow: hidden;position: relative;}

    .show_screen #image_list {padding: 0px;margin: 0px;width: 800px;position: absolute;list-style: none;}
    .show_screen #image_list li {float: left;width: 200px;height: 200px;}

</style>

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<br> var _currentIndex = 0;<br> function moveImageList(_v){<br> _currentIndex += _v;<br> if(_currentIndex &lt;-3){<br> _currentIndex = -3;<br> }else if(_currentIndex &gt; 0){<br> _currentIndex = 0;<br> }<br> var _imageList = document.getElementById(&#39;image_list&#39;);<br> _imageList.style.left = _currentIndex*200+&quot;px&quot;;<br> }<br>