A regenerative braking system includes a capacitor which is electrically connected to a stack and is charged by the stack, a traction motor, a motor control unit which control electric power input to the traction motor and electric power output from the traction motor, a chopper which is connected to the capacitor so as to be ON and OFF switched thereby limiting charging voltage of the capacitor, a braking resistor which consumes regenerative energy so as to serve as an auxiliary brake, and a hybrid control unit which turns on the chopper in case that a charging voltage limit of capacitor is exceeded so as to control overcharge of the capacitor and turns off the chopper in case that charging voltage of the capacitor descends. The capacitor is preferably a super capacitor.