An occupant detection apparatus, installed in a vehicle, including a seat belt configured to be extendable and rewindable, and to be worn by an occupant sitting on a seat of a vehicle, and a motor configured to rewind the seat belt, includes a counter electromotive force determination unit configured to determine whether a counter electromotive force is generated in the motor; and an occupant determination unit configured to determine whether the occupant sitting on the seat in the vehicle is wearing the seat belt, based on a determination result by the counter electromotive force determination unit while the vehicle is traveling.