To provide a seat back fixture that can prevent backlash of a seat back in a locked state, while minimizing the occupation area of the floor space.

The seat back fixture 4 that fixes a striker 1b of a seat back frame is fixed through an attachment hole 4a bolted and fastened to the inner wall surface of the vehicle body. A cutout 6a is formed in a lock plate 6 and an aperture 6b is prepared at an upper part. Moreover, a hook 8 is mounted rotatably by a pivot shaft 8d in the surface side of the lock plate 6. A first hook part 8b and a second hook part 8c are formed in this hook 8. A pawl part 10c that projects from a through-hole 6c becomes an engagement outside of the hook 8 in the condition that the striker 1b is set in between the first and the second hook parts 8b and 8c, and set in the cutouts 6a. This pawl part 10c is integrally formed in the elastic member and composed to appear and disappear in the vehicle width direction.