A disk cartridge includes: a pair of disk housing portions, housing a disk entirely when put together; a supporting base member with a disk housing rotating and supporting portion for rotating and supporting the housing portions to open or shut a window to the disk such that the disk gets chucked externally, and a head can access the disk and read and write information from/on the storage layer thereof, though the window; and a locking unit including a pair of locking lever portions to keep the housing portions closed from rotating and a locking lever supporting portion supporting the lever portions rotatably and attached to the base member, wherein the pair of disk housing portions open the window wide enough to remove the disk while the lock unit is not inserted into the supporting base member, and contact with the lock unit and have their angle of rotation limited while the lock unit is inserted into the supporting base member, thereby controlling the size of the window such that the disk is unremovable.