A heat treatment device where intervals between substrates supported by a supporter is reduced so that the number of substrates to be treated can be increased. A heat treatment device has a reaction furnace for treating substrates and a supporter for supporting the substrates in plural stages in the reaction furnace. The supporter has supporting plates in contact with the substrates and supporting members for supporting the supporting plates. A supporting plate and a supporting member are superposed on each other at least a part in the thickness direction.
