submit can't send data of textarea

Recently I study html and javascript. I know that in html form sends data to server between and .

However, in my case it doesn't.

here is my code

function wReply() {
             if(document.getElementById("repInputContent").value == "")  {
                alert("type anything for reply");
                document.getElementById("repInputContent").focus();
                return;
             }
             document.reply.submit();
        }

this is javascript function that work with input type button.

And this is html form code

<tr id="replyInput">
                    <td colspan="3">
                    <form action="/wReply" accept-charset="utf-8" name="reply" method="post">
                        <input type="hidden" name="num" value="<%=num%>">
                        <input type="hidden" name="writer" value="<%=writer%>">
                        <input type="hidden" name="page" value="<%=page%>">
                        <textarea rows="4" cols="40" id="repInputContent"></textarea>
                    </form>
                    </td>
                    <td><input type="button" value="submit" onclick="wReply()"></td>
            </tr>

I code a table and want to send hidden type datas and textarea data. I think it works but actually server can receive hidden type datas.

What is the problem?