The recording media cartridge includes a case body formed from an upper half and a lower half, a recording medium which is rotatably accommodated in the case body, an upper engagement portion arranged in the upper half, a lower engagement portion arranged in the lower half in correspondence with the upper engagement portion and a locking member which engages the upper engagement portion with the lower engagement portion. The lower engagement portion and the upper engagement portion are engaged with each other by the locking member whereby the upper half and the lower half are coupled with each other.