Disclosed are a servo writer and a servo writing method capable of writing a servo signal onto a servo band of a magnetic tape in an excellent condition, regardless of the thickness of the magnetic tape. The servo writer includes a magnetic tape traveling system for traveling a magnetic tape, a DC erase head for magnetizing a servo band of the magnetic tape in one direction along the length of the magnetic tape, a servo signal write head for writing a servo signal onto the servo band in the direction opposite to the one direction, a servo signal read head for reading the servo signal from the servo band, and control device for controlling a degauss current supplied to the DC erase head, based on an output read from the servo signal by the servo signal read head.