A mold for insert molding, which houses an electronic unit including a first circuit portion and a second circuit portion protruding from the first circuit portion, is prepared. The mold includes an upper wall surface facing an upper surface of the second circuit portion and side wall surfaces facing side surfaces of the second circuit portion. The flow resistance of a resin flowing through a space between each side surface of the second circuit portion and the corresponding side wall surface is lower than that of the resin flowing through a space between the upper surface of the second circuit portion and the upper wall surface. Then, the electronic unit is placed in the mold. Then, the resin is injected into the mold in which the electronic unit has been placed. Thus, the electronic unit and the housing in which the electronic unit is housed are integrated with each other.