An information recording medium cartridge is provided with a disc, a cartridge casing having the disc accommodated therein, first and second shutters movably mounted to the cartridge casing for opening and closing recording and/or reproducing openings arranged in right and reverse sides thereof. First and second slide members having the first and second shutters are mounted on the shutters. First and second shutter plates are provided with a shutter main body that overlaps the right side or the reverse side of the cartridge casing to open and close the opening and a slide-member mounting portion for mounting the first and second slide portions to the shutter main body at an end. The slide-member mounting portion is provided with an engaging claw, wherein when mounting the first and second slide portions, the engaging claw is engaged with a claw engagement provided to the slide portion.