PURPOSE: To avoid a dangerous condition such as a wheel lock in braking, by initiating the use of a duct from its focusing point for carrying brake fluid to a feedback cylinder and a piston means.

CONSTITUTION: A hydraulic circuit for calipers is extended to a duct 18 to pass through in a valve assembly 19 and a feedback piston means 20. Braking torque TRW is the product between a wheel radius RW and the frictional force T between a road and a wheel, and is torque FRD or more that is the product between force F applied to a brake disk by the pads of the calipers and a mean disk radius RD, unless the wheel is locked. Pressure drop in a hydraulic circuit acts so as to maintain an automatic correction and a desired condition FRD≤TRW, and also acts even for automatically lock-releasing the wheel momentary locked.