To provide a two-step locking type seat lock device capable of certainly preventing its striker from rattling using a simple and low-cost constitution.

The two-step locking type seat lock device is equipped with a base plate 11 furnished with a reception groove 12, a lock plate 13 pivoted swingingly and furnished with a first engaging groove 21 and a second engaging groove 22 capable of being engaged in with a striker 5 having intruded into the groove 12, and a rattle stopping plate 14 pivoted swingingly and furnished with a first engaging surface 14d and a second engaging surface 23a, whereby holding pinchedly is generated by the groove wall 21a of the first groove 21 and the the first engaging surface 14a of the plate 14 in the first step locking condition in which the striker 5 is engaged in with the first groove 21 and also by the groove wall 22a of the second groove 21 and the the second engaging surface 23a of the plate 14 in the second step locking condition in which the striker 5 is engaged in with the second groove 2. Thereby the striker 5 can certainly be prevented from rattling in both locking conditions.