PURPOSE: To prevent a shock transfer caused by strong hitting, by placing an edge ring provided with a stepped part on the rear side, on a circumferential part of a plate body, providing a gap between the circumferential edge base metal part and the inside part of the ring rear side, and executing spot welding to the outside part of the ring upper face.

CONSTITUTION: A stepped part 5 whose inside part 6 and outside part 7 become high and low, respectively is formed on the rear side face of an edge ring 4 which has formed a decorated pattern on the surface, a gap 8 is formed between the base metal surface of the circumferential part, and the inside part of the rear side face of the ring 4, and thereafter, spot welding (a) is executed to the outside part of the upper face of the ring 4. In this way, it can be prevented that a shock due to strong hitting at the time of the spot welding is transferred to a porcelain enamel or cloisonne enamel part, and a fault such as a crack, etc. does not occur.