To suppress vibration of a rotor, prevent noise generation and a lowering in pump performance, and reduce power loss and electric power consumption without requiring a shaft seal member.

Flanges 91, 101 are integrally projected respectively from the intermediate portions between a drive shaft 3 and a driven shaft 4, and these flanges are fitted and inserted into bearing abutting portions 42, 43 respectively projected from the inner peripheries of bearing holes 40, 41 a slight interval. Outer rings 9a, 11a of bearings 9, 11 are made to abut on the bearing abutting portions 42, 43, and are fixed respectively to the bearing holes 40, 41. Nuts 30, 31 are fastened for pressing and fixing a drive gear 5 and a driven gear 7 respectively to the inner rings 9a, 11a of the bearings 9, 11. By fastening the nuts 30, 31, the flanges 91, 101 of the drive shaft 3 and driven shaft 4 are also pressed and fixed respectively to the inner rings 9a, 11a of the bearings 9, 11.