function alertmsg() {
  alert("こんにちは！");
}

function ka(a) {
  var element = (a.target||a.srcElement);
  element.style.backgroundColor = "transparent";
}

function ma() {
  var x, y;
  var z = document.getElementsByTagName("span");
  for (x=0; x<z.length; x++) {
    y = z[x];			
    if (y.getAttribute("class") == "check") {
      y.addEventListener("click", ka, false);

    }
  }
}
window.onload = ma;