A disk cartridge includes a substantially box-shaped outer case that has an opening on one end face, and an inner case that is housed in the outer case such that the inner case can be pulled out and has a concave portion for an optical disk to be placed therein. On the recording surface of the optical disc, a light transmissive layer with a thickness of about 0. Therefore, the electrophoresis deposition is confined to local area. A reagent container is rotated during reading to facilitate identification. The first gate is disposed laterally from the body and the second gate is disposed laterally from the first gate.