function changeInventoryImg(shop_id, item_id, left_display_flg, left_display_threshold) {
  var val = document.getElementById(item_id).value;
  if (val == "") {
    document.getElementById(item_id + "_img").style.display = "none";
  } else {
    var arr = val.split(":");
    var img_link = "http://tw.rakuten-static.com/a/iv/index.php?s=" + shop_id + "&v=" + arr[0] + "&i=" + arr[1];
    if (left_display_flg == "1") {
      img_link = img_link + "&t=" + left_display_threshold;
    }
    document.getElementById(item_id + "_img").src = img_link;
    document.getElementById(item_id + "_img").style.display = "block";
    document.getElementById(item_id + "_img").style.display = "inline";
  }
}