An egress-start determining device determines a start of egress of a passenger seated in a seat of a vehicle. A completion determining device determines completion of a driver's head moving out of a door opening of the vehicle after the start of egress of the passenger. A seat-sitting-face height adjusting device adjusts a height of a sitting face of the seat in such a manner that the height is adjusted to a first height during a time from the start of egress of the passenger to the completion of the driver's head moving out of the door opening of the vehicle, and the height is adjusted to a second height after the completion of the driver's head moving out of the door opening of the vehicle.