A disk cartridge (7) of a new standard requiring a minimum design change in improving a conventional disk cartridge in which an erroneous insertion prevention groove with a specified depth is formed in the front end face of a cartridge body, comprising a cartridge body (70) having outer dimensions in common with those of the cartridge body of the conventional disk cartridge, wherein the cartridge body (70) has formed therein an erroneous insertion prevention groove (71) opened in the same position as that of the erroneous insertion prevention groove of the conventional disk cartridge and having a smaller depth along a cartridge insertion direction (A) than the conventional erroneous insertion prevention groove, and a cartridge identification groove (72) with a specified depth which is not available in the conventional disk cartridge.