According to one embodiment, the thin film forming apparatus includes a boat capable of holding two wafers, in each of which a cutout portion is provided in an outer peripheral edge portion, in a groove portion for holding a wafer in a state where back surfaces face each other. Moreover, the thin film forming apparatus includes a reactor that accommodates the boat and form a coating on each of surfaces of the two wafers by a vapor deposition reaction. The positions in the groove portion, at which the two wafers are held, respectively, are displaced in a direction parallel to the surfaces of the wafers.