A disk cartridge having a case including a first planar protion and a second planar portion which are disposed opposite to each other with a given spacing therebetween, and a plurality of walls which join the first planar portion and the second planar portion together. The case contains an information carrying disk in a rotatable manner and has an opening formed in one of the walls through which the disk can be inserted or removed. The disk cartridge has a lid mounted on the case for opening or closing the opening. The lid is formed so that an outer surface of the lid is located inside an outer surface of the wall in which the opening is formed.