When a seat belt 14 is unfastened, reactive force against treading pressure on the accelerator pedal is enhanced by a pedal reactive force enhancer 10 even if a driver tries to drive a vehicle by turning on an ignition switch 18 and pressing on the accelerator pedal. Thus, it is possible to prompt the driver to fasten the seat belt. When the seat belt is unfastened in an emergency, although the reactive force against treading pressure on the accelerator pedal is enhanced, the driver can drive the vehicle by pressing the accelerator pedal harder. In this way, the driver can deal with such emergency.