A disclosed thermal treatment apparatus includes a supporting member where plural substrates are supported in the form of shelves; a reaction tube that accommodates the supporting member within the reaction tube, and is provided with plural gas supplying pipes arranged in a side part of the reaction tube, thereby allowing a gas to flow into the reaction tube through the plural gas supplying pipes; and a first heating part that heats the plural substrates supported by the supporting member accommodated within the reaction tube, wherein the first heating part includes a slit that extends from a bottom end to a top end of the first heating part and allows the plural gas supplying pipes to go therethrough, and wherein an entire inner surface, except for the slit, of the heating part faces the side part of the reaction tube.