A vehicle seat lock device is provided. The vehicle seat lock device includes a seat lock housing, a striker, a hook member and a blocking member. The seat lock housing is configured to be fixed to one of a seat back and a vehicle body. The striker is configured to be fixed to the other of the seat back and the vehicle body. The hook member is rotatably mounted on the seat lock housing to latch and unlatch the striker by engaging and disengaging the striker, respectively. The blocking member is pivotally mounted on the seat lock housing. The blocking member pivots and contacts with the hook member to prevent the hook member from rotating and to maintain engagement between the hook member and the striker when a load that is higher than a predetermined amount is inputted to the vehicle body.