PURPOSE: To conduct heat treatment including stable film formation having high controllability of cooling the internal wall of a heat treatment chamber at a required temperature by a cooling gas introduced to an external wall.

CONSTITUTION: One part or the whole of the external wall of a heat treatment chamber is composed of double or more of multiple walls, and a cooling gas, through which radiant light can be transmitted, is introduced to clearances among the multiple walls and the internal wall of the heat treatment chamber is cooled at a required temperature. That is, nitrogen controlled at a low temperature and other gases, which have large heat capacity and through which radiant light is easy to transmit, are introduced into an inner tube 3 and an outer tube 2 as a cooling gas 8 and the temperature of the internal wall of the heat treatment chamber is kept at a low temperature and constant, and the temperature- rise and separation of moisture adhering to the internal wall of the heat treatment chamber is reduced or held constant. Accordingly, a stable atmosphere having low moisture concentration can be maintained in the heat treatment chamber, thus performing heat treatment including film formation required with high reliability.