A fuel pump is provided with a casing and a substantially disk-shaped impeller that can rotate within the casing. A group of concavities is formed in each surface of the impeller. The concavities forming the group are arranged in concentric circles with respect to the rotation axis of the impeller. A first groove is formed in a first inner surface of the casing and extends from an upstream end to a downstream end in an area that faces one group of concavities. A second groove is formed in a second inner surface of the casing and extends from an upstream end to a downstream end in an area that faces the other group of concavities. A seal portion is formed in at least one of the first and second inner surfaces of the casing and formed by one layer or a plurality of layers of thin film.