Provided is a heat insulation structure used for a vertical heat treatment apparatus that performs a heat treatment on a substrate. The vertical heat treatment apparatus includes: a processing container having a double tube structure including an inner tube and an outer tube closed upward, the processing container having an opening at a lower end thereof; a gas supply section and exhaust section provided on a lower side of the processing container; a lid configured to introduce or discharge the substrate into or from the opening and to open/close the opening; and a heating section provided to cover the processing container from an outside. The heat insulation structure is provided between the inner tube and the outer tube.