PURPOSE: To elevate heating efficiency of a heating furnace, by providing a turning chamber of heating gas, in the heating furnace provided with a ventilative heat insulating material for heat recovery of waste gas for heating, and preventing loading of the ventilative heat insulating material by sedimenting dust in the heating gas.

CONSTITUTION: When heating a substance to be heated 7 by leading combustion high temperature gas into a heating furnace 1 from a combustion chamber 4, a heating gas lead-in port 2 is provided along one side wall 13 of the heating furnace 1, and high temperature combustion gas is turned and made to go up in a turning chamber 9, and goes into the heating chamber from an upper gap 10 of a partition wall 8 and heats the substance to be heated 7. Waste gas passes through a ventilative heat insulating material 6 consisting of a ceramic porous body, heats it, and radiation heat from the heat insulating material 6 heated to a high temperature heats the substance to be heated 7, by which the heating efficiency is elevated. As for the heating gas, when it is turning in the turning chamber 9, contained dust is sedimented and is discharged from a bottom part discharge port 12, therefore, the heat insulating material 6 causes no loading, and its operation is not deteriorated.