An air ejection port for ejecting air-mixed oil is structured with a first air ejection port provided on the inner peripheral side from an inscribed circle of an outer rotor and a second air ejection port provided on the outer peripheral side from a circumscribed circle of the inner rotor, the air ejection port can have an enlarged port area as the total of area of the first air ejection port and area of the second air ejection port in a state without being in communication with either of a suction port and a discharge port, and a disadvantage that a pump chamber of a previous stroke and a pump chamber of a subsequent stroke communicate with each other through the air ejection port can be avoided.