SEAT

Provided is a seat which comprises: a seat frame (1) constituting a framework for a seat cushion or seat back; a synthetic resin hook member (7;17) having a locking portion (7a) locked to a frame member (1B) as a part of the seat frame (1); a stretchable planar elastic body (6) attached to the hook member (7;17) locked to the frame member (1B) so as to be mounted to the seat frame (1) in a tensioned state; and an anti-expansion mechanism for avoiding a situation where the hook member (7;17) is expanded and thereby the hook member (7;17) is disengaged from the frame member (1B).