An oil pump in which pulsation vibration due to the dynamic pressure on the discharge port side can be attenuated. In an oil pump for transporting fluid from a suction port to a discharge port by the rotation of a rotor mounted in a pump casing, a resonator configured from an introduction path and a chamber is formed with respect to a discharge flow channel that communicates with the discharge port in the flow direction of the discharge flow channel. A channel in a direction different to the flow direction of the discharge flow channel is communicatingly formed in the vicinity of the resonator.