To attain miniaturization and high efficiency and hold an initial position at the time of non-operation by rotating a partition valve by oil pressure fed to an oil pressure chamber, taking its motion off to an output shaft, and providing an output shaft rotating position detecting means on the anti- output-end side.

The base part of a partition valve 4 is fixed to a rotor 3, and the peripheral edge slides along the internal wall of a case 1. A rotating angle sensor 15 is connected to a connecting shaft 2a provided on the anti-output-end side of an output shaft 2. When the output shaft 2 is rotated by oil pressure, a bush 15f connected to the connecting shaft 2a is rotated, and a brush 15c slides within a range from A to B on an electric resistor 15b. An electric signal corresponding to the rotating angle of the output shaft 2 is outputted, and a hydraulic control valve is controlled by a computer to act so that the rotating position of the output shaft 2 comes in a target position. Miniaturization and high accuracy can therefore be attained, and the output shaft is regulated into an initial position of rotation by mounting an elastic spring onto the end of the output shaft, or the like so as to improve positioning accuracy in the non- operating state of oil pressure.