A fuel pump includes an output shaft of a motor and an impeller configured to rotate integrally with the output shaft. An outer periphery of the output shaft includes a first flat portion for engaging with the impeller. The impeller includes a through hole at a center thereof, the through hole being larger than an outer diameter of the output shaft and including a second flat portion for engaging with the output shaft. In this fuel pump, when the output shaft and the impeller are arranged coaxially, spots exist which have different lengths of a gap between the first flat portion and the second flat portion in a rotational axis direction of the output shaft.