Attachment structure of spring unit

In a seat back frame formed by attaching a spring unit (20) to a frame body (10), the spring unit (20) is easily attached to the frame without performing caulking. A projecting hooked portion (21) is formed in one side of the spring unit, and an insertion hole (13C) that receives the hooked portion (21) therein is provided in the frame. Thus, the hooked portion (21) is inserted into the insertion hole (13C) and hooked at a position on the rear surface thereof.