Abstract: A structure for preventing misinsertion of disc cartridges includes an inclined face formed at one side of the front end face of a shell of a disc cartridge of first format and for contacting a misinsertion preventing member of a superordinate drive, a groove formed in a shell of a disc cartridge of second format in the position corresponding to the inclined face and for engaging with the misinsertion preventing member, and a groove formed in a shell of a disc cartridge of third format in the same way as the disc cartridge of second format. The misinsertion preventing member, which is arranged with a cartridge holder of the superordinate drive, contacts the inclined face to disallow insertion of the disc cartridge of first format up to the position of releasing locking of a trigger lever of a cartridge-holder slide plate.