To substantially eliminate deficiencies such as portions of the resinous coating, where the film thickness is reduced considerably during the press-fitting, and to aim at providing a high productivity with a reduced cost and without the possibility of occurrence of rusting after a prolonged time of use under severe environmental conditions due to an excellent anticorrosive property, a magnetic encoder (10) includes a multipolar magnet (14) having a plurality of alternating magnetic poles alternating with each other in a direction circumferentially thereof, and a core metal (11) supporting the multipolar magnet (14). The multipolar magnet (14) is formed of a sintered element prepared by mixing and sintering a powdery mixture of a magnetic powder and a non-magnetic metallic powder. The multipolar magnet (14) is fixed on the core metal (1) by staking a portion of the core metal (11), and a sintered element/core metal assembly (21) fixed on the core metal (11) is surface treated to have with an anticorrosive resinous coating (22) for anticorrosive purpose. When the magnetic encoder is press-fitted on an encoder carrier member, one of a press-fitting punch and the magnetic encoder (10) is heated to a temperature within the range of 60 to 150.degree. C.