To reduce a manufacturing cost and realize stably both reduction in leak flow in a pump section and reduction in sliding resistance.

Seal layers 52, 54 are arranged on both inner surfaces of casing pumps 38, 40 respectively facing the front and bock sides of an impeller 36. The seal layers 52, 54 are formed by stacking a single-layer thin film or multiple layers of thin films. The formation of a seal layer by a thin film is easy and low in cost as compared with the formation of a seal layer by using a cutting operation and is high in processing accuracy despite of these facts. Consequently, both the reduction in leak flow and the reduction in sliding resistance can be stably realized.