PURPOSE: To elevate further fuel saving rate by passing the combustion air consumed by a burner provided on a heating zone through recuperator provided to a cooling zone to receive the waste heat of a material to be heated.

CONSTITUTION: The recuperator 5 is for instance provided in a slow cooling room 3 and by passing the air fed forcibly thereto from a blower 7 through the recuperator 5, the preheated air is used as a combustion air for a burner 6 provided in a heating room 2. The belt-shaped material 1 to be heated is passed in order through a preheating room 8 having a flue duct 9, heating room 2, slow cooling room 3 and cooling room 4 of a continuous heat treating furnace wherein the material 1 is transferred with a floating system and heat treated with preheating, heating, slow cooling and cooling.