diff --git a/FO/Views/Account/Join.cshtml b/FO/Views/Account/Join.cshtml
index 3aaeb33..68e5c64 100644
--- a/FO/Views/Account/Join.cshtml
+++ b/FO/Views/Account/Join.cshtml
@@ -62,7 +62,7 @@ else
                 <li><input type="password" id="userpass2" placeholder="비밀번호확인"></li>
                 <li>
                     <ul class="jnNum">
-                        <li><input type="text" id="userpno1" maxlength="6" class="int nocomma" value="@((Model.User.birthday ?? "").Substring(2))" @(!string.IsNullOrEmpty(Model.User.birthday) ? Html.Raw("readonly=\"\" style=\"background-color:#ddd;\"") : Html.Raw(""))></li>
+                        <li><input type="text" id="userpno1" maxlength="6" class="int nocomma" value="@(!string.IsNullOrEmpty(Model.User.birthday) && Model.User.birthday.Length > 3 ? (Model.User.birthday ?? "").Substring(2) : "")" @(!string.IsNullOrEmpty(Model.User.birthday) ? Html.Raw("readonly=\"\" style=\"background-color:#ddd;\"") : Html.Raw(""))></li>
                         <li>-</li>
                         <li><input type="tel" id="userpno2" maxlength="7"  class="int nocomma" placeholder="주민등록번호 뒤 7자리"></li>
                     </ul>