PURPOSE: To enable the supply of a uniformly distributed gas to a reaction element and thereby to make an improvement in terms of the nonuniformity in film thickness within a surface of a wafer and among wafers, by fitting a baffle plate between a reaction gas supply element and the reaction element in a reaction element tube made of quartz.

CONSTITUTION: Two reaction gas blowoff ports 5 are provided in a reaction gas supply element 10 on the front cap side of a reaction element tube 1 made of quartz, and they are constructed so that two kinds of reaction gases for forming a film are blown off therethrough. The two kinds of reaction gases supplied through the reaction gas blowoff ports 5 are to be led directly toward a reaction element 11 by the exhaustion on the rear side, but their path is blocked by a baffle plate 6 for mixing. Consequently spontaneous stirring occurs and the mixing is made in this part. The reaction gases mixed herein strike then against a baffle plate 7 for diffusion. This baffle plate 7 for diffusion is provided with many holes 8 distributed evenly in a section of the advancing reaction gases, and therefore the evenly distributed reaction gases can be supplied to the reaction element 11.