A library apparatus in which a plurality of cell drums are divided into two groups respectively placed on the left and right side of a recording/reproducing unit placed in a central part thereof. In this library apparatus, rails are placed in a direction along which the cell drums and the recording/reproducing unit are arranged. The conveying of media, which are contained in the cell drums placed on the left side of the recording/reproducing unit, is assigned to an accessor placed on the left side thereof. Simultaneously, the conveying of media, which are contained in the cell drums placed on the right side of the recording/reproducing unit, is assigned to an accessor placed on the right side thereof. A robot hand of each of the accessors is opened and closed by a turn of a motor. At that time, a power supply is turned off. Moreover, the robot hand is prevented by a locking mechanism from popping out of the accessor. Furthermore, ordinary cartridges are discriminated from cleaning cartridges.