The invention provides a tape library wherein the accommodated number of cassette tapes can be adjusted freely. Where one or more expansion units are connected to a basic unit, when a transport mechanism is positioned within the basic unit, a control circuit section of the basic unit controls the position and operation of the transport mechanism with reference to a position reference point of the basic unit, but when the transport mechanism is within an expansion unit, the control circuit section controls the position and operation of the transport mechanism with reference to a position reference point of the expansion unit. The control circuit section and the transparent mechanism of the basic unit are interconnected by a flat cable like an elongated belt which includes a plurality of conductors extending in parallel to each other and joined together with an insulating material, and when an expansion unit is coupled, the cable for interconnecting the transport mechanism and the control circuit section need not be replaced. This allows smooth coupling of an expansion unit and smooth transportation of a recording medium in the expansion unit to a recording and/or playback section by the transport mechanism of the basic unit.