Abstract: A disk case has a pocket-shaped case body for accommodating a disk. Tongue pieces are provided at one edge of the case body, at the centers of opposite halves of the periphery of a disk insertion inlet thereat. These tongue pieces are formed so that one end of each is aligned with a corresponding end of the other at a first position of the end of the disk insertion inlet, and overlap or cross each other on the outside of the periphery. The respective other ends of the tongue pieces coincide with a pair of opposite edges of the case body. Perforations are provided along the boundary between each of the tongue pieces and the case body. The tongue pieces can be torn at these perforations to be separated from the case body. The disk case thus formed has a simple structure, can be easily sealed and appended to a book, and prevents a disk from moving in the case after being placed therein.