An impeller rotates for pressurizing fluid in a pump passage. The impeller includes an inner circumferential portion and an outer circumferential portion. The outer circumferential portion has two axial end surfaces that respectively have a plurality of vane grooves arranged in a rotative direction of the outer circumferential portion. A plurality of communication holes axially penetrates one of the inner circumferential portion and the outer circumferential portion. The plurality of communication holes is displaced from the plurality of vane grooves in a radial direction of the outer circumferential portion. The plurality of communication holes is arranged substantially along the rotative direction of the outer circumferential portion at nonuniform pitches.