PURPOSE: To improve the oil lubrication effect between a fitting hole of a thrust suppressing plate and a driving groove on a driving shaft by interposing a thrust suppressing plate between the bottom part of a thrust suppressing plate accommodation chamber and the edge surfaces of an inner rotor and an outer rotor.

CONSTITUTION: As for an oil pump device which is prepared by arranging an inner rotor 4 and an outer rotor 5 in a rotor accommodation chamber C, a thrust suppressing plate 20 is shaped into a flat plate, and rotatably fitted into a fitting groove 21A drilled in a ring form on a driving shaft 21, while there are drilled a fitting hole 20A, first groove 20B opened in correspondence with a suction passage 6A of a pump cover 2, and the second groove 20C opened in correspondence with a discharge passage 6B. The thrust suppressing plate 20 is arranged so that the first groove 20B corresponds to the suction passage 6A, and the second groove 20C corresponds to the discharge passage 6B, in the suppressing plate accommodation chamber 30B of a pump cover 30. A portion of the oil which flows into the suction passage 6A is introduced into the fitting hole 20A through the first groove 20B and a driving shaft insertion hole 20D, and the oil lubrication between the fitting groove 21A and the fitting hole 20A is carried out.