Japanese Laid-Open Patent Publication No. 2008-44080 discloses a hydraulic torque wrench that includes a power transmitting apparatus. The power transmitting apparatus comprises a cylinder filled with hydraulic oil. The cylinder is located inside an outer casing part and is rotated by a drive motor via a rear-side planetary gear mechanism. A bearing that rotatably supports the cylinder is disposed between a small diameter portion of a rear part of the cylinder and the outer casing part, and an internal gear of the planetary gear mechanism is disposed on the rear side of the bearing.
The outer casing part of this device is formed of metal and further comprises: a housing that houses the motor, an outer wall of the planetary gear mechanism disposed on the front side of the housing, and a case of the cylinder disposed on the front side of the outer wall.