PURPOSE: To restrain a temperature rise at the periphery of a cylindrical shell main body consisting of a cylindrical thin metal plate by heat distribution through the metal cylindrical shell main body, increase the thermal efficiency for reducing fuel consumption, and improve the heat-insulating property by a method wherein heat- insulating material is applied on at least inner surface of the cylindrical shell.

CONSTITUTION: During heating, a burner 10 is ignited to directly heat a can main body 6c from the bottom by a flame spouted from the burner 10. As the lower end of a partition plate 9 is lower than the bottom of the can main body 6c, hot-air produced by the flame of the burner 10 rises through only an inner space which faces the outer face of the can main body 6c, so that a canned food 6 can be efficiently heated and the heat amount which passes along an outer cylindrical shell 2 is reduce. During heating, the partition plate 9 directly contacts with combustion gas and is heated to high temperatures and the heat is transferred from the partition plate 9 to a heat-insulating material 21 through the joint part on the periphery side. Since the heat-insulating material 21 has a heat-insulating and heat-storing properties, heat is gradually transferred to an outer cylindrical shell main body 22 at a reduced heat transfer rate.