To provide a small size and lightweight fluid pump capable of being practically used from a low rotation speed to a high rotation speed and good in energy efficiency.

A rotation cylinder 2 having a perfect circle outer circumference surface 17, a double head piston 3, and a drive shaft 1 having an eccentric shaft are combined in a casing 4 having a perfect circle inner circumference surface 16, a drive shaft gear 1b and a cylinder inner gear 2a are meshed and volume of a space part 27 formed between the piston 3, the cylinder 2 and the casing 4 is expanded and contracted by rotating a drive shaft. This rotary pump performs suction and delivery through a suction port 22 and a delivery port 21 leading to the outer circumference from the inner circumference surface 16 of the casing 4 by change of the volume.