To obtain brake torque of an almost constant size from low speed to high speed and obtain an excellent response at the time of an operation by arranging a viscous fluid coupling and a clutch between a car body side member and a rotating member on the side of an engine in series.

A viscous fluid coupling 5 is provided between a housing 3 and a clutch hub 17. The housing 3 and the clutch hub 17 are provided with concentric circular projecting parts 21, 23 and recessed parts 25, 27. Between these projecting parts 21, 23 and recessed parts 25, 27, a pressure chamber 29 is formed. In this pressure chamber 29, silicone oil is filled. When air pressure is fed to a cylinder part 37, a multiple disc clutch 7 is fastened by being pressed by a piston 35 via a bearing 39 and a pressing member 41. At this time, the relative revolution of the multiple disc clutch 7 and the piston 35 is absorbed by the bearing 39. When the multiple disc clutch 7 is fastened at the time of braking a vehicle, revolution of a drive shaft 13 (wheel) is absorbed by the viscous fluid couling 5 via the multiple disc clutch 7 and braking force is strengthened.