An accessor device for a tape library has two accessor bases movably mounted on two parallel guide rails extending along a plurality of cells housing tapes. The accessor bases have, on respective confronting portions thereof, overlapping edges which overlap each other in a direction normal to the longitudinal direction of the guide rails when the accessor bases move toward each other. The accessor device mounted on the two parallel guide rails is prevented from falling, and the accessor devices with the overlapping edges has a wide accessible area for accessing endmost regions in the tape library.