PURPOSE: To supply excellent oil having few bubbles by obtaining high bubble removing effect without providing a specific bubble removing device outside a pump.

CONSTITUTION: An outer rotor 5 and an inner rotor 7 are supported in a relatively rotatable manner. Oil is fed from a suction port 2 to a discharge port 3 accompanied with volume variation of a pump chamber 9 between internal and external gears 6, 8 which are meshed with each other. A through-hole 10 formed on the internal gear 6 of the outer rotor 5 is communicated with the pump chamber 9 between the internal and external gears 6 and 8. A bubble discharge passage 11 is communicated with the through-hole 10 accompanied with the rotation of the rotors 5 and 7. When the external gear 8 approaches the internal gear 6 acceleratingly together with the rotation of the rotors 5, 7, inertia reartion is generated on the oil inside the pump chamber 9. Specific gravity of the oil excluding bubbles is larger than that of the bubbles, so that the inertia reaction of the oil is larger than that of the bubbles. The bubbles having small specific gravity tend to gather around the internal gear 6. The gathered bubbles are discharged from the discharge passage 11 through the through-hole 10 on the internal gear 6.