A seat height control amount setting part determines a target seat height displacement amount according to a deceleration outputted from a braking state calculating part. The deceleration is corrected according to the vehicle speed of a vehicle, and the target seat displacement amount is set such that the seat height becomes lower as the vehicle speed is higher. While correcting the target seat height displacement amount, a target deceleration with respect to the amount of operation of a brake pedal is corrected. The target deceleration is corrected such that the target deceleration with respect to the amount of operation of the brake pedal becomes greater as the vehicle speed is higher.