打开php文件直接下载了

初学PHP，写了很简单的代码，可是浏览器打开时把PHP文件直接下载了，估计是apache环境有问题，该怎么搞大家帮忙看下<html>
    <form action="test.php" method="POST">
        <table>
            <tr>
                <td>Name: <input type="text" name="name" size=10 maxlength=10></td>
                <td><input type="submit" value="Submit"></td>
            </tr>
        </table>
    </form>
</html>
<html>
    <body>
        <?php
            $name = $_POST['name'];
            echo 'isset($name)'.isset($name).'<br />';
            echo 'isempty($name)'.empty($name).'<br />';
            echo 'isset($null)'.isset($isnull).'<br />';
            echo 'isempty($null)'.empty($isnull).'<br />';
        ?>
    </body>
</html>