A disk cartridge accommodating a disk-type recording medium (1c) and adapted to be used on a recording/read-out apparatus having at least an upper head and a lower head for making access to the upper and lower surfaces of the disk. The disk cartridge comprises an upper case member (1a) and a lower case member (1b) which are assembled together to form a case defining therein an internal space for accommodating the disk. Head windows (2a, 2b) formed in the upper and lower case members such as to oppose to each other so as to allow the heads to make access to the disk therethrough, the head windows extending in a predetermined radial direction of the disk. A recess formed by recessing the surface of each case member at a region extending between one longitudinal end of the head window and the edge of the case member closest to the longitudinal end of the head window. A shutter (3) capable of sliding on the case in the widthwise direction of the head windows so as to open/close the recesses and the head windows. The head window formed in the upper case member and the head window formed in the lower case member has different widths. This disk cartridge enables the shutter to be stably supported on the case, and reduces the risk for the disk to be contaminated by foreign matters.