A servo write head assembly comprises an AC demagnetizing head that slides in contact with a magnetic tape all of which surface is magnetized in one direction of longitudinal directions thereof, and demagnetizes a data band of the magnetic tape; a servo write head that slides in contact with the magnetic tape, magnetizes a servo band of the magnetic tape in a reverse direction, and writes a servo signal; and a guide for regulating a movement in lateral directions of the magnetic tape that is running, wherein the AC demagnetizing head and the servo write head are integrally configured and the guide is provided between the AC demagnetizing head and the servo write head.