except that the honeycomb structure of the comparative example does not have a gap 14 each of the honeycomb heaters produced in example and comparative example was arranged in an exhaust tube of an engine installed on a bench downstream of the honeycomb heater was arranged a commercial catalyst element having a cylindrical shape of 3 66 inches in diameter and 1 3 liters in volume the catalyst element includes a monolithic structure and a catalyst composition loaded thereon then a durability test was conducted for 100 hours under conditions that an exhaust gas was introduced into the honeycomb heater at a temperature of 850 u00b0 c according to a fuel cut mode in which the fuel supply to the engine was cut temporarily every one minute each of the honeycomb heaters of example and comparative example was arranged at a manifold position which is about 400 mm downstream of the discharge port in the exhaust system of an engine of 2 000 cc a port for introducing secondary air was provided downstream of the honeycomb heater downstream of the honeycomb heater was provided the catalyst element subjected to the above durability test a battery of 12 volts was arranged so as to apply electric current to the honeycomb heater bag emission was measured in.