There is provided an electric heater support plate which is not likely to be softened or deformed during firing at a high temperature, even if a material to be fired contains an alkaline component or an Si component as a volatile component. A passage 2 for the material to be fired surrounded by a ceiling refractory 11, wall refractories 12 and a floor refractory 13 is provided with an electric heater 3 heating from above and an electric heater 5 heating from below. This electric heater 3 has at least its heating part 31 mounted and supported on a fire-resistant support plate 4, and this support plate 4 in this invention has a two-layer structure in which an insulating ceramic support plate 41 is laminated on an SiC-based ceramic plate 42. The two-layer structure support plates 4 are supported by refractories 14 installed in a furnace and are arranged in parallel in a plurality of rows in a longitudinal direction of the furnace, and the electric heater 3 mounted on the support plates is so constructed as to generate heat by an electric power supplied from an energizing terminal 32 exposed to the outside of a furnace wall.