Disclosed are a magnetic tape cartridge and a servo writer which both allow a magnetic tape drive to recognize a level of a voltage signal being read from a servo signal. In a magnetic tape included in the magnetic tape cartridge, a servo signal that has been written on a servo band contains output level data indicating an output level of the servo signal itself. The magnetic tape drive reads the servo signal, then extracts the output level data therefrom, and adjusts the output level of the servo signal to a predetermined level.