Object of this invention is to provide a servo writer capable of automatically controlling record current amount supplied to a writing head for every kind of magnetic tape when writing a servo signal on many kinds of magnetic tapes. The servo writer for writing a servo signal on magnetic tape MT which is fed out from a feeding reel and taken-up by a take-up reel includes writing head H1 that writes a servo signal on the magnetic tape MT, inspection head H2 for reading the servo signal formed on the downstream side and written on the magnetic tape MT, servo signal inspection part 16 that inspects the servo signal read by the inspection head H2, and current amount control part 17 that controls the amount of record current supplied to the writing head H1 based on the inspection result in the servo signal inspection part 16.