PURPOSE: To reduce noises by constituting pilot gears by fitting helical gears which have the same twist direction with a couple of helical gear rotators to one end part of their rotating shafts.

CONSTITUTION: Helical gear rotators 1 and 2 having the same waveform curve are arranged rotatably through thrust bearings 6, 6... in a rotator storage chamber 5 which has an inflow port 3 and an outflow port 4 while engaging each other. Pilot gears 7 and 8 are constituted by fitting the helical gears which has the same twist directions with the rotators 1 and 2 to the rotating shaft 9 and 10 projecting from the storage chamber 5 in one body. When fluid flows in from the intake 3, the rotators 1 and 2 are applied with the pressure of the fluid and then the rotators 1 and 2 and pilot gears 7 and 8 come together to form a couple of single helical gears; and axial displacement due to a thrust load operating on the rotators alternately in absorbed to smooth the rotation. Consequently, the noise level in operation is lowered and, specially, rasping noises of high frequency are reduce extremely.