A pump unit includes an insertion guide member that extends in a longitudinal direction of the pump unit and is used to guide the pump unit at a time of inserting the pump unit into an opening portion of a fuel tank. The insertion guide member includes a stopper portion and a guide portion that are arranged along an edge part of the insertion guide member. When the pump unit is projected in the longitudinal direction onto a plane of projection, the stopper portion protrudes outward from an imaginary circle, which has a fitting portion's diameter, on the plane of projection. The guide portion guides the pump unit in a rotational direction relative to a stay. A cross section of the pump unit taken along a guide portion orthogonal plane is set to be within the imaginary circle, which has the fitting portion's diameter.