The lock device for a vehicle in accordance with the present invention comprises a synthetic resin body fixed to a door and equipped with a recess formed on its right side; a latch fitted rotatably into the recess; a striker fixed to a car body and having a front leg portion having a small diameter and meshing with the latch, a rear side leg portion having a large diameter and a wedge-like bridge portion connecting the tips of the leg portions and having a thin front portion and a thick rear portion; a guide groove formed on the body and permitting the entrance of the striker; front side clamp means disposed on the front side of the guide groove, for clamping the front side of the striker; and rear side clamp means disposed on the rear side of the guide groove, for clamping the rear side portion of the striker. A swell portion defining the guide groove is formed integrally on the back side of the body and a metallic back plate is fixed to this back side. A plurality of retainers for receiving the swell force to the swell portion, that occurs when the striker is clamped, are formed on the back plate.