A rotary pump has a linear groove formed on an end surface of a second side plate of an outer rotor. Thereby, it becomes possible to generate a force for pushing back the outer rotor to a sealing member side, and thus it becomes possible to reduce load applied to the second side plate. As a result, contact resistance between the outer rotor and the second side plate becomes smaller, and smoother pumping operation becomes possible. Further, since the force for pushing back the outer rotor to the first sealing member side is generated in the linear groove, it is possible to reduce an amount of decrease in a contacting area with the outer rotor and the second side plate, thereby reducing an amount of wear of the outer rotor and the second side plate.