To generate the braking force of different levels and to reduce the size in a rotary fluid pressure actuating device (a geroter motor) having a brake.

This rotary fluid pressure actuating device has an output shaft 39 rotatable with respect to a fluid displacing mechanism and a housing 41. The device has first and second brake disks 51, 53 for braking the output shaft 39. The brake disks 51, 53 are engaged by an actuating piston 59 energized to an engaged state by a coned disk spring 85. The actuating piston 59 partitions a first pressure chamber 73 from a second pressure chamber 75, and the coned disk spring 85 is disposed in the first pressure chamber 73. When both pressure chambers 73 and 75 are exhausted, the actuating piston 59 is energized only by the coned disk spring 85. However, when the first pressure chamber 73 is pressurized, the actuating piston 59 is energized by a substantially larger force, thus resulting in the generation of a larger braking torque.