For heating a mold efficiently and uniformly and for protecting an induction coil from corrosive gases, an upper plate that contacts an upper end face of a mold, and a lower plate that contacts a lower end face of the mold are provided, and an induction coil, provided to each plate, has a voltage applied by a commercial power supply. Each plate has a metal plate body in which a recessed housing portion that houses the induction coil is formed, and a cover that closes the recessed housing portion in a state where the induction coil is housed therein. A cover placement portion having a step that is greater than or equal to the thickness of the metal cover is formed in the metal plate body, and a plurality of jacket chambers in which a gas-liquid two phase heating medium is enclosed are formed in the metal plate body.