An occupant protection device of the present invention includes a knee-protecting airbag device and a container box. The airbag device includes an airbag for protecting knees of an occupant seated in front passenger's seat, an inflator, and a case opened rearward for housing the airbag and the inflator. The container box includes a box body and a lid. Before being mounted on the vehicle, the knee-protecting airbag device and the container box are integrally assembled into a mounting module. By mounting the module on the vehicle, the knee-protecting airbag device and the container box are mounted on the vehicle. The occupant protection device of the present invention contributes to reduce tact time per vehicle even if the knee-protecting airbag device and the container box are both mounted in front of front passenger's seat.