A rotational speed of an electric motor 12 is memorized at a memory unit 21 as a set rotational speed for allowing a minimum required volume of brake fluid to be discharged from the pumps in a state where the output hydraulic pressure of the master cylinder is highest, and an energizing duty ratio for the electric motor 12 which is designed so as to rotate the electric motor 12 at the set rotational speed is determined at a duty ratio determining unit 22 in response to an applied voltage detected at a voltage detecting unit 20. A motor control unit 23 controls the energizing of the electric motor 12 from a battery 18 in accordance with the energizing duty ratio determined at the duty ratio determining unit 22.