PURPOSE: To simplify installation, by inserting a set of friction plates on a fixed side and friction plates on a rotary side from inside to engage same with an inside wall of a rear axle housing, inserting an actuator and fixing a ball cam plate.

CONSTITUTION: Friction plates 59 on a rotary side are provided on a brake shaft 51R, while friction plates 58 on a fixed side are engaged with a rear axle housing H, and both the plates are alternatively arranged. An actuator 55 is provided inside of the friction plates, and a set of these members is fitted to a bore E of the rear axle housing H. A ball cam plate 56 is fixed through a ball 57 to the clutch housing H. The actuator 55 is rotated through an arm shaft 53R and a crank 54R by rotation of a brake arm 52R.