PURPOSE: To boost the braking force with the use of magnetic force, by providing such an arrangement that the supply of current to an electromagnetic means is controlled in accordance with a detection signal indicating the depressing force of a brake pedal to generate an electromagnetic force corresponding to the depressing force of the pedal.

CONSTITUTION: When a brake pedal 5 is depressed, the depressing force is detected by a depressing force detecting means 7 which issues an output signal to a control means 9. This control means 9 therefore supplies current to an electromagnetic solenoid 8 in an electromagnetic means 6 in accordance with the depressing force. With this arrangement the electromagnetic means 6 is driven so that a master cylinder is operated under the electromagnetic force.