To provide a
servo writer that reduces the number of cartridges to be discarded.SOLUTION: A
servo writer 210 for a
cartridge 10 includes: a traveling portion that feeds out a tape-shaped magnetic recording medium (
magnetic tape MT) from the
cartridge and winds the feed magnetic recording medium to make the magnetic recording medium travel; a demagnetizing
magnet 214 that erases a first
servo pattern formed on the traveling magnetic recording medium; a servo
signal writing head 215 that writes a servo
signal onto the traveling magnetic recording medium after the first servo pattern is erased and forms a second servo pattern; and a control device that controls the head to write the servo
signal during at least one of acceleration and deceleration traveling periods of the magnetic recording medium and forms the second servo pattern that does not satisfy the standard on the magnetic recording medium.SELECTED DRAWING: Figure 8