The pump housing includes a pair of sliding surfaces clamping the outer and inner gears from both their sides to allow both the gears to slide on the sliding surfaces, a suction port part suctioning fuel from outside into inside of the gear accommodation chamber, and a discharge port part discharging fuel from inside into outside of the gear accommodation chamber. At least one of the suction port part and the discharge port part includes an elongated groove that is depressed from the corresponding sliding surface and extends along a circumferential direction of the pump housing in a region opposed to the pump chambers, opening bores that open on the elongated groove from outside of the gear accommodation chamber, and ribs each of which is arranged between the corresponding adjacent two opening bores. The opening bores and the ribs are arranged alternately along an extending direction of the elongated groove.