PURPOSE: To provide a pump device which facilitates machining and assembly and improves performance of a pump through reduction of a gap size between gear rotor and a case.

CONSTITUTION: A pump device comprises a case 10, first and second gear rotors 12 and 14 rotatably held in the liquid feed chamber 10a of the case 10, a gear 16 for external teeth geared with internal teeth 12a arranged on the inner side of the first gear rotator 12, a rotary shaft 18 on which a gear 16 for internal teeth is supported rotatably around an axis, and an liquid inflow port 20 and a liquid outflow port 22. In which case, the two gear rotors 12 and 14 are pressed against the inner wall of the liquid feed chamber 10a as the rotors are not supported rotatably around an axis, and rotated in a state that the addendum of a tooth makes contact with the inner wall of the liquid feed chamber 10a.