Abstract: An information memory unit includes a cartridge and an information memory medium rotatably arranged in the cartridge. The cartridge has a cartridge body having first and second surface walls facing each other. A shutter is slidably mounted on the cartridge body and includes a first shielding portion located on the first surface wall, for opening and closing a first opening portion formed in the first surface wall, a second shielding portion located on the second surface wall, for opening and closing a second opening portion formed in the second surface wall, and a coupling portion connecting the first and second shielding portions. The first and second shielding portions has guide projections which are engaged first and second guide grooves formed in the first and second surface walls, respectively.