To provide a variable displacement piston pump motor with which it is possible to obtain an adequate discharge quantity and to obtain a power transmitting device for a vehicle with which it is possible, by making use of it, to obtain an adequate differential limiting force even when the difference in number of revolution is small.

A reardef 1, and variable displacement piston pump motors 5 and 7 disposed respectively on the output sides of a carrier case 3 are provided, respective suction ports 5a and 7a of the respective pump motors 5 and 7 are communicated with discharge ports 7b and 5b of the other respective pump motors 7 and 5, a rotor 59 which is driven by output shafts 41 and 43 and a cam ring attached to the case 3 are provided, and the capacity is controlled by steplessly deforming the shape of the cam ring by a servo motor 73 through a movable board 63 in response to the travelling state of a vehicle.