These materials are thoroughly mixed by means of a mixing machine such as a Henschel mixer or a ball mill, thereafter the mixture obtained is melt-kneaded by means of a heat kneader such as a heat roll kneader or an extruder to make the resins melt one another, in which the wax and the magnetic material are dispersed, and this kneaded product is cooled to solidify, followed by pulverization and cl