<div id="ara">
<form action="">
<input id="burayagelsin" value="" type="text" name="ara">
<select id="selectsec" onchange="changeFunc(this.value);"></select>
<option value="secenek1">Seçenek 1</option>
<option value="secenek2">Seçenek 2</option>
<input type="submit" name="submit" value="Ara" />
</form>
</div>


<script>
function changeFunc(i) {
document.getElementById("burayagelsin").value = i;
}
</script>