Welcome Wenzheng Ke! Are you Chinese? I'm curious because of your name. We have very few members from Asia.
In any case, yes, it's legitimate, but it was made in an Indonesian factory as shown. We have a member Ralf
@SFIV1967 who's much more familiar with the factories Guild used and their serial number systems. Your photo is a great help.
It appears to be one of the modern ( 2015 or later?) re-issues. You may have seen original versions from the '60's on line.
I'm not too familiar with Guild electrics in general, so I could be mistaken. Other members will offer more advice soon. You came to the right place!