To make it possible to ensure a large quantity of circulating amount at a high temperature with low power by making it possible to generate strong circulating flow at a high temperature.

This air flow furnace comprises heat sources 3A, 3B for heating circulating gas out of the furnace, and an outdoor circulating route 4 for taking out the combustion gas in the furnace 18 out of the furnace and again circulating it from another place into the furnace 18. The route 4 has thermal storage units 5A, 5B provided at exits/entrances 9A, 9B to a heating chamber 2, a circulation fan 6, a channel switching unit 7 selectively coupled to the one of the units 5A, 5B at the suction port side and discharge port side of the fan 6 to relatively switch the direction of the flow of the air to the units 5A, 5B and means 8 for extracting heat or dilute to alter the gaseous state of the flow in the route 4 between the units 5A and 5B. Burners 3 for heat sources are alternately burned, and a high temperature forcible circulating flow 10 for periodically inverting the flowing direction of the flow by the unit 7 in synchronization with the combustion of the burner 3 is formed in the furnace 2.