Each adapter disposed on a rack includes a pair of arms that configure an opening/closing mechanism. During rack conveyance, a guiding block is slotted between a pair of legs contained in the rack. The opening/closing mechanism being abutted against the guiding block causes the opening/closing mechanism to perform an opening/closing operation. When the state of the opening/closing mechanism is changed from closed to open, a pre-measurement sample container is passed from a sample storage unit to a lifting mechanism. Subsequent to the post-measurement sample container being returned to the sample storage unit, the state of the opening/closing mechanism is changed from open to closed.