<p>A magnetic tape cartridge includes a cartridge casing formed by upper and lower casing halves connected together, and a single reel around which a magnetic tape with a leader pin fixed to the leading end of the magnetic tape is wound and which is contained in the cartridge casing for rotation. The leader pin is removably held in a tape draw-out opening with its axial direction directed in the vertical direction under urging force of a spring member acting on its upper and lower end portions sideways with the upper and lower end portions received in recesses respectively formed in the upper and lower casing halves. An improved spring member mounting structure is provided. <IMAGE>A magnetic tape cartridge includes a cartridge casing formed by upper and lower casing halves connected together, and a single reel around which a magnetic tape with a leader pin fixed to the leading end of the magnetic tape is wound and which is contained in the cartridge casing for rotation. The leader pin is removably held in a tape draw-out opening with its axial direction directed in the vertical direction under urging force of a spring member acting on its upper and lower end portions sideways with the upper and lower end portions received in recesses respectively formed in the upper and lower casing halves. An improved spring member mounting structure is provided. <IMAGE></p>
