PURPOSE: To prevent repeated dent of a side and an end surfaces, to simplify manufacture, and to prevent the occurrence of deformation, by a method wherein a metallic sheet, e.g. an iron sheet, is deep drawn, and an ion or out embossed part for reinforcement is formed on each of both sides and both end surfaces.

CONSTITUTION: An oblong in embossed part 5 is formed in the vertical surface region of each side 3 of a deep drawn body 1, and simultaneously a square in embossed part 6 in the vertical surface region of each end surface 4. A firewood inlet 8 through which to feed firewood and a primary air intake 9 are formed in the embossed part on the front end surface, and an exhaust port 10 is formed in the embossed part on the rear end surface. A hole 12 through which an intake pipe 11 for feeding secondary air is caused to pass is formed, and the intake pipes 11 and 11 are secured to the inside of each side of the body by welding and machine screws. Further, when the inside is burnt by using firewood, in order to prevent escape of combustion heat directly through the exhaust port 10, a baffle plate 13 is mounted to the inside of a rear end surface with a distance between the exhaust port 10 and the baffle plate.