A cartridge case for containing a disk-shaped recording medium has a shutter attached slidably thereon. The shutter is U-shaped sectionally and the edge sections where the shutter contacts the surface of the cartridge case are rounded so that friction therebetween is reduced when the shutter slides on the surface of the cartridge case. The cartridge case is provided with a notch and an indentation on at least one of its side surfaces corresponding to protruding pieces in the device into which the cartridge case is inserted such that a sensor in the device can be activated only when a cartridge case compatible with the device is inserted and these protruding pieces properly engage with the notch and the indentation on the cartridge case.
