First, an inner tube member is accommodated in an outer tube member. Then, rigid powder, having high rigidity and a hard-to-magnetize characteristic, into the inner tube member. Next, magnetic powder is filled into a recessed portion of the inner tube member. Then, the inner tube member is drawn out of the outer tube member. Then, a composite filler composed of the rigid powder, magnetic powder and outer tube member is subjected to a cold hydrostatic pressure pressing process as pre-processing. Next, the composite filler is heated and solidified into a billet. Then, the billet is subjected to a hot extrusion process so that it is formed into a bar-shaped workpiece. The bar-shaped workpiece is rolled onto a roller, and then the outer tube member is peeled off. Next, the bar-shaped workpiece is subjected to a cutting process so that it is formed into an elongated bar. Then, a magnetic section of the elongated bar is magnetized into a scale structure.