PURPOSE: To sufficiently ensure a braking capacity for emergency braking in addition to stable braking for continuous service by pinching with pressure N-pieces (N=1 or 2) of rotors when a first actuator is put in operation and pinching with pressure (N+1) pieces of rotors when a second actuator is put in operation.

CONSTITUTION: For the time of service braking, oil pressure is introduced from a hydraulic system for exclusive continuous service braking to a cylinder 18, so that pushing force is added by a piston 19 to rotors (13) and stators (14) via a pressure plate 16. At this time, when the number of rotors in use (N) is 1, for example, two pieces of stators 14, 14, counted from the left, are caught by a stopper 24, so that only one, left-end rotor 13 is effectively pinched. Meanwhile, for the time of emergency braking, high oil pressure from hydraulic system for exclusive emergency braking is introduced into a cylinder 21, so that pushing force is added by a piston 22 to rotors (13) and stators (14) via a pressure plate 17. At this time, the stopper 24 does not work as a stopper, but all the rotors 13 including the one, left-end rotor (13) for the time of service braking are pinched by the stator 14.