function comp_select_view() {
	var obj = document.getElementsByClassName('item_comp_check');
	var i, count;

	count = 0;
	for (i = 0; i < obj.length; i ++) {
		if (true == obj[i].checked) {
			count ++;
		}
	}

	if (2 == count || 3 == count || 4 == count) {
		return true;
	} else {
		alert('比較は２つから４つまでです。');
		return false;
	}
}
function comp_select_all() {
	var obj = document.getElementsByClassName('item_comp_check');
	var i;

	for (i = 0; i < obj.length; i ++) {
		obj[i].checked = true;
	}
}
function comp_select_free() {
	var obj = document.getElementsByClassName('item_comp_check');
	var i;

	for (i = 0; i < obj.length; i ++) {
		obj[i].checked = false;
	}
}