[bes]

<div id="myDiv">
<input type="button" value="-">
<input type="text" id="inp" size="1" value="1" disabled>
<input type="button" value="+"><br>
<input type="button" value="-">
<input type="text" id="inp" size="1" value="1" disabled>
<input type="button" value="+"><br>
<input type="button" value="-">
<input type="text" id="inp" size="1" value="1" disabled>
<input type="button" value="+"><br>
</div>

<script>
window.onload = function () {
  var myDiv = document.getElementById('myDiv');
  var inp;

  myDiv.onclick = function (e) {//onclick begin
    e = e || event
    var target = e.target || e.srcElement;
    if (target.value == '+') {
      inp = target.previousSibling.previousSibling;//previousElementSibling лучше, но не для IE<9
      if (parseInt(inp.value) < 5) {
        inp.value = parseInt(inp.value) + 1;
      }
    } else if (target.value == '-') {
      inp = target.nextSibling.nextSibling;//nextElementSibling лучше, но не для IE<9
      if (parseInt(inp.value) > 1) {
        inp.value = parseInt(inp.value) - 1;
      }
    }
  }//onclick end

}
</script>