function readCookie(name) {
  allcookie = document.cookie + ';'
  start1 = allcookie.indexOf(name);
  if (start1 != -1) {
    target = allcookie.substring(start1, allcookie.length);
    start2 = target.indexOf('=', 0) + 1;
    end = target.indexOf(';', start2);
    return(unescape(target.substring(start2, end)));
  }
  return("");
}
function writeCookie(name, value) {
  expdays = 30;
  t = new Date;
  t.setTime(t.getTime() + expdays * 24 * 60 * 60 * 1000);
  document.cookie = name + '=' + escape(value) + '; expires=' + t.toGMTString();
}
function clearCookie(name) {
  if (document.cookie != "") {
    t = new Date;
    t.setTime(t.getTime() - 1 * 24 * 60 * 60 * 1000);
    document.cookie = name + '= ; expires=' + t.toGMTString();
  }
  alert('このページに関するCookieを消去しました');
}