PURPOSE: To obviate the disturbance in the sequence that magnetized parts of different polarities appear alternately in the longitudinal direction even in the joint parts with the magnetic scale of the next one unit length and to maintain the accurate inter-scale spacings even in the joints between the magnetic scales of each one unit length with simple work.

CONSTITUTION: Long-sized ribbon-like magnetic recording media 51 are disposed in such a way that their respective one ends are arranged evenly with respect to a magnetizer 60. When electric current is supplied to a coil 63, the media 51 are vertically magnetized in the positions corresponding to projecting parts 62 and 2n pieces of magnetized parts 53 differing in polarities alternately are formed in the longitudinal direction, whereby the magnetic scale of one unit length is magnetized. The magnetized parts 53a, 53b at both ends of said unit length are mutually reversed in the magnetization directions. While the relative positions of the magnetizer 60 and DMEs 56, 57 are held maintained, the long- sized media 51 formed with the magnetic scale by one unit length are fed approximately by one unit length in an arrow A direction and the unmagnetized parts of the media 51 are positioned on the magnetizer 60 so as to be formed with the magnetic scale of the next one unit length.