In an oil pump apparatus, a drain outlet is positioned outwardly from an inner peripheral surface of a suction passage or from an extended line thereof at a sectional view which takes along an orthogonal direction relative to a central axis of the suction passage and which shows the drain outlet, and/or the drain outlet is positioned at a side of a shaft aperture to be away from an imaginary line connecting a central axis of a discharged passage and a central axis of the suction passage at a sectional view which takes in parallel with the central axis of suction passage and which shows the drain outlet, such that the opening center of the drain outlet is not overlapped on the imaginary line.