A manufacturing method for an actuator including a casing and a housing. The method includes setting a metallic ring in a molding die; injection molding a first flange portion of the casing using one annular hooking piece of the metallic ring as a part of a surface of the molding die so as to outsert-mold the metallic ring on a molded surface of the first flange portion, the molded surface being opposite to a first connecting end surface of the first flange portion; engaging the first flange portion with a second flange portion of the housing so as to be opposed to each other; and applying force to bend the metallic ring to form an other annular hooking piece, thereby crimping and fixing the first connecting end surface of the casing with a second connecting end surface of the housing.