A vertical heat treatment apparatus enabling the insertion of a temperature sensor in the reaction tube without disassembling the apparatus is disclosed. The vertical heat treatment apparatus includes a reaction tube; a heating section; a wafer holding section; a supporting section movably provided in the vertical direction so as to seal the reaction tube while the wafer holding section is in the reaction tube; a temperature sensor insertion section provided in the supporting section and having a through hole for guiding a temperature sensor so that the temperature sensor can be inserted into the reaction tube; and a cap section for opening and closing the through hole of the temperature sensor insertion section while the wafer holding section is on the supporting section.