A disk cartridge, which is compact, which requires a small number of parts, and which is easily assembled, is provided. The disk cartridge of the present invention comprises an upper case and a lower case. Each of the upper case and the lower case is formed to be substantially circular. The upper case and the lower case define a disk-accommodating section when the lower case and the lower case overlap with each other. The disk cartridge is opened/closed by rotating the upper case relative to the lower case about a base point of a movable section which is provided for the upper case and/or the lower case. An information-recording disk is accommodated and removed in a state in which the disk cartridge is open. The disk cartridge further comprises an engaging section for engaging the upper case and the lower case with each other and an opening for exposing a central portion and an information-recording surface of the information-recording disk, the opening being formed at least on surfaces of the upper case and the lower case.