PURPOSE: To make it possible to utilize the exhaust heat effectively from combustion gas by providing a heat exchanger in the exhaust gas cylinder of a device which burns wastes such as garbage, etc. by high frequency heating.

CONSTITUTION: A garbage receiving vessel 2 in which wastes such as garbage 17 are received is received in a primary combustion chamber 1, and, when a magnetron 3 is oscillated, microwaves are transmitted on an electricity conducting tube 4 and emitted to garbage 10 in the primary combustion chamber 1. With this arrangement the garbage 17 is heated and dried, and the gases that are generated during the garbage drying go though a nozzle filter 6 and moves to a secondary combustion chamber 5, where they are mixed with the combustion air and burn. After this the combustion gases are cleaned of odor, CO or NO2, etc. in them and go to an exhaust gas diluting chamber 8 and there they are mixed with a large volume of air and pass through a heat exchanger 9 to be discharged. The incineration of the garbage 17 continues as described above, and when a hot water temperature sensor 12 which is provided in the outlet of the heat exchanger 9 indicates an upper limit point, a hot water delivery solenoid valve 13 opens and the hot water in the heat exchanger 9 is sent to a water storage tank 14.