The invention relates to a case (10) for disk cartridges comprising a containing part (1) adapted to contain the disk cartridges (D), and a lid part (2) which is provided on an opening (1a) of the containing part (1) via a hinge part (3) and adapted to be freely opened and closed. There are provided at least one pair of locking portions (6a), (6b) which are adapted to be engaged with each other in areas near corners (c) of both side faces of the opening (1a) of the containing part (1) and an opening (2a) of the lid part (2). Therefore, the invention has made it possible to provide the case which can be simply manufactured and can obtain sufficient lock holding force required for practical use.