PURPOSE: To miniaturize a motor and to heighten torque by constituting a revolving valve of a gerotor hydraulic device to have inside and outside openings in cooperation with a two-way passage valve opening in a main body and to be connected so as to revolve together with an oscillating stick, with an inside valve opening divided.

CONSTITUTION: A revolving valve 60 has four inside valve openings 61 and an outside valve notch 62 and these cooperates with five valve openings 70 of a valve plate so as to perform a valve operation. The revolving valve 60 revolves together with an oscillating stick 34 and a separated and recessed notch 62 improves an outside opening valve operation. The shape of the opening 61 is determined by a locus tracked by a specified valve opening 70 of the moving valve 60, an extended part 65 on the outermost side of the opening 61 is at a radial outside of the opening of the revolving valve 60, and area of a valve liquid passage between the opening 61 and the valve opening 70 is increased. By the combination with the valve 60 to be fitted into the oscillating stick 34, the revolving valve 60 can be made larger than other parts and valve accuracy is improved.