To suppress looseness of a striker engaged with a seat back provided on a slide device in a reclining device for a vehicle seat.

A backrest angle of a seat back 2 is fixed by engaging a lock device 10 with a striker 22D of a slide device 20 provided on a vehicular side wall Bo (vehicle body). The striker 22D is provided on a movable side rail 22 to slide with the movable side rail 22 relative to a fixed side rail 21, thereby changing the backrest angle of the seat back 2. An engagement pin 22F2 integrally provided on the striker 22D slides along a circular arc guide groove 21C2 formed on the fixed side rail 21 to oscillate, thereby absorbing a movement amount of the deviation between the striker 22D and the lock device 10 in the height direction.