Abstract: A method of fusion bonding of a mark plate places a mark plate, having a heat-melt portion formed on at least a part of a front surface-outer peripheral portion, a side surface and a back surface-outer peripheral portion, the heat-melt portion being made of a thermoplastic resin 6, into a recess portion provided on a surface of a wall plate. A peripheral portion of the mark plate is heated to a temperature not lower than the melting point of the thermoplastic resin from the front surface side of the wall plate by a front surface side heater, e.g. a heating platen 7, while heating the peripheral portion of the mark plate to a temperature not higher than the melting point of the wall plate from the back surface side of the wall plate by a back surface side heater, e.g. another heating platen.