To provide a heat treatment apparatus capable of stacking heated objects in high density to apply heat treatment with the narrow spacing of stacking stages for stacking the heated objects.

The heat treatment apparatus has a heat treatment chamber into which hot air generated in a hot air supply means is led. A gondola with a large number of stacking stages 56 fixed at vertically equal spaces to a gondola frame, is arranged in the heat treatment chamber. The stacking stage 56 is provided with a substrate support mechanism 53 comprising a lifting mechanism 52 and a support body 50 disposed inside a frame member 57. The substrate support mechanism 53 can advance/retreat the support body 50 from the surface of the frame member 57 by regulating air pressure in an air chamber 60 by an air pressure regulating means to extend/contract a cylindrical body 62.