A recording tape cartridge. An operation protrusion of an inadvertent erasure prevention plug is inserted into an operation hole, which is formed in a lower case, and exposed to the outside. The operation protrusion is operated in a first direction or a second direction, and thus permission for recording to a recording medium which is accommodated in the case is switched by movement of the inadvertent erasure prevention plug in the first direction or the second direction within the case. At edge portions of the operation hole toward the first direction and the second direction, recess portions communicate with the respective edge portions. Floors of the recess portions are defined by thin-wall straight portions at which an outer face of an angled rear wall of the case is recessed in parallel with an inner face thereof.