A pump includes a second housing member in which a suction-side groove and a discharge-side groove are formed at a predetermined interval in a circumferential direction of a bottom of a pump chamber so as to be recessed in the bottom of the pump chamber. Fitting portions that are fitted to bosses are formed on an outer surface of the second housing member. A protruding portion, which overlaps with the bosses in a thickness direction, is formed so as to protrude from a surface of the housing on which the fitting portions are formed. A relief valve is provided in the protruding portion, and the relief valve discharges fluid from the discharge-side groove when pressure in the discharge-side groove is equal to or higher than predetermined pressure.