PCT No. PCT/JP96/00503 Sec. 371 Date Sep. 10, 1997 Sec. 102(e) Date Sep. 10, 1997 PCT Filed Mar. 1, 1996 PCT Pub. No. WO96/28843 PCT Pub. Date Sep. 19, 1996In a thermal treatment apparatus that accommodates substrates to be processed (W) in multiple stages within a reaction tube (4) and subjects them to a thermal treatment, thermal protection members (19) are provided around the peripheries of the substrates (W) to be processed to intercept thermal radiation that is incident on the peripheral edge portions thereof at a predetermined angle of incidence or greater. The peripheral edge portions of substrates (W) to be processed are generally more readily affected by thermal radiation as the angle of incidence of thermal radiation thereon increases, but, since thermal radiation from the heater at a predetermined angle of incidence ( theta ) or greater is intercepted by the thus disposed thermal protection members (19), the effects on thermal radiation on the peripheral edge portions of the substrates (W) to be processed are controlled. As a result, the temperature difference within the surface between the central portion and peripheral edge portion of each substrate to be processed (W) can be sufficiently reduced, not only under normal pressure within the reaction tube (4) but also under reduced pressures, and thus the temperature can be raised or lowered rapidly, enabling an increase in throughput.