To provide a heat treatment furnace capable of shortening a time necessary for replacing an initial furnace atmosphere with a desired furnace atmosphere, precisely performing the replacement, and lowering a concentration of residual initial furnace atmospheric gas in comparison with a conventional one, for example, when the furnace atmosphere is replaced with a nitrogen gas.

In this heat treatment furnace, a refractory 2 having air permeability, is mounted along a wall face of a furnace wall 1 at the inside of the furnace wall 1. A clearance 3 is formed between the furnace wall 1 and the refractory 2, and a gas for adjusting the atmosphere, of a specific composition introduced into the clearance 3 is sent into the furnace through the inside of the refractor 2, in adjusting the furnace atmosphere.