A servo writer is provided, which applies DC magnetization to a zone of a magnetic tape that is in advance subjected to AC erasing and writes a servo signal onto the DC magnetized zone. The servo writer has a DC erasing head and a servo signal writing head. The DC erasing head conducts DC erasing by applying DC magnetization to the magnetic tape which travels past the DC erasing head. The servo signal writing head writes the servo signal onto the magnetic tape downstream relative to the DC erasing head in a direction of traveling of the magnetic tape. In this servo writer, one of the DC erasing head and the servo signal writing head has an integrally formed flange which is able to restrict widthwise misalignment of the magnetic tape.