A thermal insulator can change a heat insulation characteristic partially with a simple structure. The thermal insulator is divided into a plurality of parts in accordance with a temperature of a heat source which is insulated by the thermal insulator. The plurality of parts are formed of different honeycomb structures, respectively, so as to provide different heat insulation characteristics. The plurality of parts may be formed by different materials, or a shape or dimension such as a cell pitch of the honeycomb structure may be varied. Heat is collected from air within the honeycomb cells, and is transferred to other parts for heating.