An apparatus and a method for manufacturing a reactor capable of both absorbing a dimensional variation of a core and preventing deformation due to a resin pressure during molding are provided. An apparatus for manufacturing a reactor is provided with a core. The apparatus includes a mold including a cavity for housing the core. The mold includes a plurality of pins protruding into the cavity. When the core is disposed in the cavity, at least one of the plurality of pins is not fixed, and each of the pins functions as a positioning pin. When a molded article is molded, the pin is fixed, and each pin functions as a core support pin for supporting the core against a resin pressure during molding.