PURPOSE: To eliminate necessity for a bolt when an actuator support member of a parking mechanism is mounted.

CONSTITUTION: An almost cylindrical actuator support member 18, by holding it interposed by a casing main unit 10 and a housing 12 from both ends in an axial direction, is locked in the axial direction. The actuator support member 18, by fitting together its protrusive part 18b to a groove 10a of the casing main unit 10, is locked in the direction of rotation. In this way, without using bolts, the actuator support member 18 can be fitted.