PURPOSE: To prevent a hydraulic fluid being used in each unit from being mixed as well as to make the hydraulic fluid separately usable for each unit, by installing an oil seal between two pump units set up in series inside a housing.

CONSTITUTION: Two large and small pump units 10 and 12 are set up in series inside a housing 8 consisting of a center body 2 and each of longitudinal covers 4 and 6. And, each pump unit is constituted of each two sheet of plates 14, 16 and 18, 6, rings 26 and 28 being held between these plates and connected by pins 22 and 24, and both rotors 30 and 32 rotating in each ring, and these rotors is rotated by drive shafts 34 and 36 piercing each shaft center. And, these drive shafts 34 and 36 are interlocked and connected with each other via a coupling 46. At this time, an oil seal 64 is installed between these pump units 10 and 12, and thereby both units are completely separated from each other, while separate hydraulic fluid is made so as to be usable for both.