There is constructed a constitution including an exhaust gas fired regenerator constituting a heat source by exhaust gas from an external machine generating the exhaust gas, an introducing flow path for guiding the exhaust gas to the exhaust gas fired regenerator, an exhaust flow path for exhausting the exhaust gas from the exhaust gas fired regenerator, a bypass flow path branched from the introducing flow path, flow path switching device including a first damper provided at the introducing flow path and a second damper provided at the bypass flow path for switching flow of the exhaust gas to the introducing flow path and the bypass flow path, a damper provided at the exhaust flow path for cutting off the exhaust gas from flowing in the exhaust flow path and gas delivering device for blowing a gas to a portion of the exhaust flow path between the damper for cutting off the exhaust gas from flowing and the exhaust gas fired regenerator.