To provide a method for heating a material to be treated at uniformly distributed temperatures along a longitudinal direction of the material in a heat-treating furnace.

The heat-treating furnace has a heat treatment chamber 2 longitudinally sectioned into a plurality of control zones, a heating means 5 for heating an atmospheric gas in the heat treatment chamber 2 and a circulating means 4 for circulating the atmospheric gas heated by the heating means 5 as hot blast. The method for heating a material to be treated includes supplying the hot blast from one side of the material in a width direction to the other side in the above heat treating furnace; measuring each temperature of the hot blast in the respective control zones (i = 1 to n), specifically each temperature in upstream ((t) in upstream (i)) and each temperature in downstream ((t) in downstream (i)); and controlling an air quantity (Qi) of the circulating means in the respective control zones so that the difference of the temperatures (Δti=(t) in upstream (i)-(t) in downstream (i)) becomes equal.