OIL PUMP

An oil pump (1) is provided with an inner rotor (22) configured to rotate integral with a shaft (20), an outer rotor (23) disposed in a loose-fit state within a pump chamber (31) and having an internal toothed portion provided on an inner periphery of the outer rotor and meshed with an external toothed portion provided on an outer periphery of the inner rotor (22), a ring-shaped pressure chamber (34) provided adjacent to the pump chamber (31) in a direction of a rotation axis (X), a discharge opening (241) for connecting the pump chamber (31) and the pressure chamber (34), and a discharge passage (35) having one end (35b) connected to the pressure chamber (34) and the other end serving as a connection opening (35a). The discharge passage (35) is formed to have a circular cross-sectional shape when viewed in the rotation axis X direction, and is provided at a position bridging the inside and outside of the outer periphery of the pressure chamber (34) when viewed in the rotation axis (X) direction. The one end (35b) of the discharge passage (35) is provided at a position reaching to a middle of the pressure chamber (34) when viewed in a radial direction of the rotation axis (X), and the discharge passage (35) and the pressure chamber (34) are in direct communication with each other.