A first piston (65) that presses friction plates (69a, 69c) is fitted in a second piston (66) in such a manner as to be movable together with the second piston and relatively movable with respect to the second piston. An A-chamber (61) and a B-chamber (62) each configured to move a respective one of the first piston (65) and the second piston (66) by a stroke toward a side close to the friction plates, a return spring (161) biasing the second piston (66) on a side away from the friction plates, and a stopper member (160) configured to prevent a stroke of the second piston (66) toward the side close to the friction plates from becoming greater than a given value (W) are provided. Engagement responsiveness of a L-R brake (60) does not deteriorate even when a clearance (V) in the friction plates (69a, 69c) increases.