An occupant protection device includes: a collision prediction unit configured to predict a collision state including a collision direction in a vehicle; a seat direction detection unit configured to detect a direction of a seat that is rotatable around a vertical axis of the vehicle with respect to the vehicle; a driving unit configured to adjust a degree of tension of a seatbelt; and a control unit configured to control the driving unit in accordance with the collision direction with respect to the vehicle predicted by the collision prediction unit and the direction of the seat with respect to the vehicle detected by the seat direction detection unit to change the degree of tension of the seatbelt.