A cartridge main body (34) formed by halves (32, 33) for housing a disc (31) having a magnetic member (30) at its centre is provided with a recess (82) in the underside of the upper half (32), the recess being formed by spaced annular lugs (81, 82) which can engage the disc (31) and the magnetic member (32) respectively so that a projection on the disc formed when the magnetic is secured thereto does not contact the disc half (32) and produce debris. Reinforcing projecting ribs (84 a , 84 b ) and reinforcing projections (88, 89) are provided on the halves (32, 33) of the main body (34) in the vicinity of apertures (39, 40) for insertion of a recording/reproducing head of recording/reproducing apparatus and in the vicinity of an adjacent side edge of the cartridge main body (34) along which a shutter (41) can be slid to cover or not to cover the apertures (39, 40). A shutter locking member (47), provided with a portion (60) of flexible material, can pivot on the housing half (33) and is engaged by an engaging part (48) of the shutter (41).