PURPOSE: To aim at the shortening of each drive shaft and the solution of strength shortage or the like due to bending, by connecting these drive shafts in plural pump units set up in series inside a housing, with a connecting member after being divided.

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 each of drive shafts 34 and 36 piercing each shaft center. At this time, these drive shafts 34 and 36 are interlocked and connected with each other via a coupling 46. And, each spline 60 is formed in an inner surface of this coupling 46 and each outer surface of these shafts 34 and 36,whereby transmission of driving force is carried out.