To provide a heat treatment apparatus capable of effectively preventing the deformation of a chamber caused by heat even if treating a substrate at a high temperature.

The heat treatment apparatus has a triple structure in which a chamber 1, a second chamber 2 and a frame cover 3 are arranged outwardly successively in this order. In the chamber 1, a hot plate 4 for heating and processing a substrate 100 is arranged. The second chamber 2 includes: an upper lid 21, a body 22 and a hood 26 each of which is composed of a metal sheet; and heat insulating materials 23 arranged on inner surfaces of the upper lid 21, the body 22 and the hood 26. In the second chamber 2, there are formed a chamber base 27 and a heat insulation area TI surrounding the chamber 1. In other words, there is formed the heat insulation area TI composed of an air heat insulation layer in which the circulation of air with the outside is limited between the chamber 1 and the second chamber 2.