To improve heat insulation, the yield of substrate processing, and quality without increasing the entire length of a heat insulator of a substrate holding tool for holding a substrate to be processed and without increasing the number of heat insulating sheets used in the heat insulation part in a heat treatment apparatus.

The heat treatment apparatus comprises a treatment chamber 22 for accommodating and treating a substrate; a heater for heating the treatment chamber; and a substrate holding tool 21 for holding a desired number of the substrates in the treatment chamber. The substrate holding tool includes a substrate holder for holding the substrate; and a heat insulator located below the substrate holder and including a desired number of heat insulation plates, with a pitch of the heat insulation plate located above the heat insulator made smaller than that of the heat insulation plate of a lower part of the same.