http://codepen.io/eond/pen/kztDK


html

<form name="form" id="form" method="post">

    <select onchange="input();" id="sel" name="sel">

        <option value="" selected="selected">은행</option>

        <option value="대구은행 715-12-12423423 정낙훈">대구은행</option>

        <option value="농협 758-12-156966 정낙훈">농협</option>

        <option value="우리은행 054-332-9900">우리은행</option>

    </select>

    <input type="text" id="box" name="box" class="FORM1" size="20" value="" readonly="readonly" />


css

input{border:0;width:500px;text-align:right}


js

function input(){

    var kim = document.getElementById("sel").value;

    document.getElementById("box").value = kim;

}