Disclosed herein is a magnetic tape cartridge comprising a single reel with magnetic tape wound thereon, a cartridge case for rotatably housing the single reel, a leader pin having a tape clamp portion on which the magnetic tape is wound, and a clamp member with a C cross section that has an axial slit. The leader pin is affixed to a leading end of the magnetic tape by elastically fitting the clamp member onto the tape clamp portion of the leader pin. A sheet member for enhancing a coefficient of friction is interposed at least between the magnetic tape and the tape clamp portion.