To provide a heat treatment method capable of being executed even in a heat treatment furnace capable of improving productivity per an installation area of the furnace in heat treatment for a sheet-form substance, such as a solar battery substance, etc., and capable of being executed even in a heat treatment furnace not using a conveying means, such as a mesh belt, being high in thermal capacity.

The method is a method to effect heat treatment of a sheet-form substrate in a radiation heating type heat treatment furnace provided at an upper part in the furnace with a heating means. The two sheet-form substrates make one set, the two sheet-form substrates 1a and 1b of each set are positioned opposite to each other, and supported in a valley-form state that an upper part is opened and a low part is closed, and contained in the furnace to perform heat treatment.