A recording tape cartridge in which an ability to assemble a security tag into a case is excellent is provided. A recording tape cartridge includes: a case that accommodates a reel on which a recording tape is wound; a security tag having a substantially pillar shape, that is provided within the case, and that is adapted to transmit to and receive from an exterior; and a holding portion formed in the case, that holds the security tag by having the security tag fitted with the holding portion.