A slide mechanism for a shutter, installed on a cartridge case of a disk cartridge, which is slidable in both right and left directions relative to the cartridge case from a neutral position at which a head access opening is closed by the shutter, and which is constituted by a smaller number of components and easy to assemble. The case has a groove which forms between a pair of counterparts forming the case itself; the shutter is biased toward a neutral position at which the shutter closes the head access opening; and the shutter has a projecting part which slidably engages the groove. The shutter is divided by a connecting portion of the upper wall side shutter plate and the lower wall side shutter plate, and the shutter is fixed together after the shutter plates are assembled to the cartridge case.