Can't create any folder in /var/www/ with new user for Wordpress, but can edit files and names (Also all permissions got), Ubuntu 14.04

Hi, I can’t create any folder in /var/www/ directory, via my new Wordpress user

Here is permissions of that user.

-rw-rwxr-- 1 wp-user wp-user 418 Sep 24 2013 index.php -rw-rwxr-- 1 wp-user wp-user 19930 Apr 9 19:50 license.txt -rw-rwxr-- 1 wp-user wp-user 7194 Aug 6 14:27 readme.html -rw-rwxr-- 1 wp-user wp-user 4896 Dec 24 2013 wp-activate.php drwxrwxr-x 9 wp-user wp-user 4096 Aug 6 14:41 wp-admin -rw-rwxr-- 1 wp-user wp-user 271 Jan 8 2012 wp-blog-header.php -rw-rwxr-- 1 wp-user wp-user 4818 Feb 18 16:45 wp-comments-post.php -rw-rwxr-- 1 wp-user wp-user 3591 Aug 11 15:32 wp-config.php drwxrwxr-x 4 wp-user wp-user 4096 Aug 6 14:41 wp-content -rw-rwxr-- 1 wp-user wp-user 2932 Sep 24 2013 wp-cron.php drwxrwxr-x 12 wp-user wp-user 4096 Aug 6 14:41 wp-includes -rw-rwxr-- 1 wp-user wp-user 2380 Oct 24 2013 wp-links-opml.php -rw-rwxr-- 1 wp-user wp-user 2359 Oct 24 2013 wp-load.php -rw-rwxr-- 1 wp-user wp-user 33407 Aug 6 02:37 wp-login.php -rw-rwxr-- 1 wp-user wp-user 8235 Nov 13 2013 wp-mail.php -rw-rwxr-- 1 wp-user wp-user 11070 Apr 7 16:15 wp-settings.php -rw-rwxr-- 1 wp-user wp-user 25665 Nov 12 2013 wp-signup.php -rw-rwxr-- 1 wp-user wp-user 4026 Oct 24 2013 wp-trackback.php -rw-rwxr-- 1 wp-user wp-user 3032 Feb 9 2014 xmlrpc.php

What am I doing wrong?

Thanks!