A locking mechanism for locking an outer shell includes a frame adapted to be stacked with an outer shell and having a through hole for extension of an engaging piece of the outer shell therethrough, a locking element disposed movably on the frame, and a release button disposed slidably on the frame. The locking element has a hook-engaging portion, and a contact portion opposite to the hook-engaging portion. The hook-engaging portion is extendable to the through hole for engaging releasably the engaging piece. The release button has one end abutting against the contact portion. The release button is operable to push the contact portion, which in turn moves the hook-engaging portion to disengage from the engaging piece.