PURPOSE: To improve safety of wheel braking by coaxially arranging a metal disc and a carbon disc, and simultaneously providing each of the discs with an actuator for actuating the disc, and allowing the actuator of the metal disc to be shut off by a shutoff device when a fluid pressure exceeds a limiting value.

CONSTITUTION: A metal disc 1 is formed integrally with a boss 3. A carbon disc 2 is fit with the boss 3 in such a manner that the disc 2 can freely slide in an axial direction. A caliper 9 is arranged close to a portion of outer peripheries of the discs 1, 2. The caliper 9 is provided with actuators 13, 14 arranged in housings 10, 11 defined by a partition 12 and on sides in opposition to the partition 12, and respectively comprising pistons 15, 16 biased by return springs 17, 18 in directions away from the discs 1, 2. The pistons 15, 16 and the partition 12 are respectively supported by braking linings 20 to 23. Then, when a fluid pressure exceeds a lining value, only the operation of the actuator 13 is shut off by a shutoff device 27.