Hi folks,
I installed Office 2013 without Service Pack. Then check windows update.
I get the message: Windows is up to date

Hi,

Office is not part of Windows, so you need to connect to Microsoft Update to get the updates for Office added to your machine.

After you connect to Microsoft Update, the Windows Update will do both for you.

update.microsoft.com

Hi,

In addition to Don's suggestion, another method would be to launch Windows Update like you normally do, click the "Change setting link on the left, then select the option of "Give me updates for other Microsoft products when I update Windows.". See:

Regards,

Steve Fan
TechNet Community Support