PURPOSE: To enable action of a multiple disk clutch without providing a rotation sliding part using an X ring at a passage for supplying pneumatic pressure by providing a thrust bearing between a flange mounted coaxially on an axle shaft in capable of movement in the direction parallel with the shaft and a piston.

CONSTITUTION: A multiple disk clutch 6, a cylinder 14 to which a pneumatic pressure for control is supplied, a piston 12 which is slidably in contact with the inside of this cylinder and displaced according to the pneumatic pressure, and a transmission mechanism for transmitting the displacement of this piston to the multiple disk clutch are provided. These cylinder and piston are fixed to a case 15 which covers a differential gear 11 and becomes a body not rotated against rotation of the axle shaft 3. Moreover, as a transmission mechanism, a flange 17 which is mounted coaxially on the axle shaft and can be moved in the parallel direction is provided, and a thrust bearing 18 is arranged between this flange and the piston so that the flange is moved by the pneumatic pressure received by the piston to press the multiple disk clutch through a spring means 19.