To provide a method to enable conveyance and heat treatment of a substance to be thermally treated without using a jig and a support member, such as a setter, being high in thermal capacity or without generating contamination, in a continuous type heat treatment furnace.

The method is a method where, in the continuous type heat treatment furnace, heat treatment is effected as intermittent or continuous conveyance of a plate-form substance to be treated or a substance to be thermally treated placed on a plate-form setter is performed. By feeding air or gas in a furnace through vent holes 5 formed in a furnace bed, conveyance in a furnace or heat treatment of the substance 1 to be thermally treated are effected as the substance 1 to be thermally treated or the plate-form setter on which the substance to be thermally treated is floated from a furnace floor.