Abstract: A head shutter is mounted on casing of a magnetic disk cartridge to openably cover a head insertion opening, and a spindle shutter is mounted on the cartridge casing to openably cover a spindle insertion opening. A shutter operating member is mounted on the cartridge casing, and is operable from the outside of the cartridge casing. When the insertion openings are closed, the shutter operating member is engaged with the head shutter and the spindle shutter to hold them against their opening movements, and when the insertion openings are to be opened, the shutter operating member is disengaged from the spindle shutter, and also acts on the head shutter to open the head shutter. A shutter opening-closing mechanism is provided in a disk drive unit, and includes a first shutter opening member for operating the shutter operating member, and a second shutter opening member for moving the head shutter from its half-opened position to its fully-opened position.