To simplify the structure of a motor-driven oil pump.

The oil pump 10 comprises a pump housing 11 with an oil intake port 16, an outlet port 17 and a bearing port 13a, a bearing board 13, a motor housing 12 with an opening 12a connected to the bearing port 13a, a shaft 31 journaled to the bearing part 13a, having an inner rotor 18, outer rotor 19 and a magnet 33, and a coil 34. One end of the shaft 31 extends into the pump housing 11 and the other end extends into the motor housing 12. The inner rotor and outer rotor compress the oil by their rotation. The coil 34 is located with a prescribed internal from the magnet 33 outside in the radial direction of the shaft 31 and fixed to the motor housing 12, and rotates the shaft 31.