To apply a brake by short-circuiting the opposite ends of a DC motor through a solid state element upon interruption of power supply to the driving circuit for a DC motor.

Upon interruption of power supply to a circuit 4 for driving a DC motor 2, power is fed from a capacitor C connected in parallel with the motor drive circuit 4 to a control circuit 12 thus short-circuiting the opposite ends of DC motor substantially. Consequently, the DC motor 2 can be braked continuously over a period where the capacitor C ensures a minimum operating voltage from the control circuit 12 for the DC motor 2 upon interruption of power supply from a feeder line 8. Even if the feeder line 8 is disconnected during travel, abrupt missing of steering can be prevented by resetting the rear wheel steering mechanism to neutral state slowly.