To make thickness and concentration of a film formed on a wafer surface uniform by eliminating pressure gradient of the gas ejected from each ejecting hole of a gas feed pipe in a diffusion furnace.

This vertical type diffusion furnace, has a gas feed pipe 8A, in which a plurality of gas ejecting holes 9 of a same hole diameter are arranged at equal intervals, where the gas feed pipe 8A has such structure as the cross sectional area of the gas feed pipe 8A becomes smaller as the position shifts from the lowest end (base bottom), where gas feed opening is located to the upper end (top end).