(function(){
	var slider = function(){
		var n = 0;
		var image = document.getElementById("image_slide").getElementsByTagName("ul")[0];
		var slide = function(start,end,sub_timer){
			// radian = degree/180 *pi
			var width = 641;
			var volume = end-start;
			var radius = width/2*volume; // 半径,移動量
			var x = (Math.cos(n/180*Math.PI)+1)*radius-width*(start+volume);
			n++;
			if(n==180){
				window.clearInterval(sub_timer);
				n = 0;
			}
			return x;
		}
		var flag = 0;
		var start = 0;
		var end = 0;
		var timer = window.setInterval(function(){
			switch(flag){
				case 0: flag = 1; start = 0; end = 1; break;
				case 1: flag = 2; start = 1; end = 2; break;
				case 2: flag = 0; start = 2; end = 0; break;
			}
			var sub_timer = window.setInterval(function(){
				image.style.marginLeft = slide(start,end,sub_timer)+"px";
			},1);
		},15000);
	}
	
	document.ready(slider);
})();