An electric furnace has a furnace wall, a cylindrical spiral member made of a wire of heat resistant material, a part of the cylindrical portion of which being embedded into the furnace wall and the remaining cylindrical portion of which being projected from an inner surface of the furnace wall, and a heating member inserted into the remaining cylindrical portion of the spiral member. The wire is wound along circles, ellipses, triangles, or quadrangles. The heating member has a circular, quadrangular, triangular or elliptical cross section.