A disc cartridge for freely rotatably accommodating a disc-shaped recording medium, which includes a cartridge casing having a disc chamber defined therein for freely rotatably accommodating the recording medium and also a generally U-shaped access opening defined in one of four sides of the cartridge casing, a lid assembly pivotally supported by the cartridge casing for pivotal movement about a pivot pin in a plane substantially parallel to a plane of the cartridge casing for selectively opening and closing the access opening, and a lid lock means provided between the cartridge casing and the lid assembly for locking the lid assembly in a closed position. The lid lock means includes at least one tubular boss having a through-hole defined therein, and an engagement piece accommodated within the through-hole and separably connected to the tubular boss, a part of the engagement piece protruding outwardly from one of opposite ends of the through-hole and engageable in a hole defined in one of top and bottom walls of the cartridge casing which is adjacent to said one of the opposite ends of the through-hole. That part of the engagement piece is engaged in the hole when the lid assembly is held in the closed position, but the engagement piece may be separated from the tubular boss when an external pushing force is applied thereto through the hole.