kikan = 10;      // 日数を変更する場合はこの値を適当に
icon = "<img src='http://www.nissinka.co.jp/images/new.gif' alt='new' width='26' height='13' class='new_icon' />";  // 適宜、サイズやalt属性を指定
today = new Date();
upday = new Date();
function koushin(y, m, d) {
   upday.setFullYear(y);
   m = m - 1;
   upday.setMonth(m);
   upday.setDate(d);
   difference = today.getTime() - upday.getTime();
   difference = Math.floor(difference / (1000 * 60 * 60 * 24));
   if (difference < kikan) {
      document.write(icon);
   }
}