To lower a working cost, to provide sufficient product accuracy and to reduce the problems of residual distortion as well by using a powder injection molding method for the manufacture of a yoke.

As a raw material, the powder of permalloy (weight ratio is about 8) and the powder of polystyrene (weight ratio is about 2) are mixed and kneaded well (process 1). An injection molding machine is provided, the mixture of the raw material is fused, supplied to an injection molding die, filled in a cavity having the shape of a product and then cooled in the molding die to harden the resin (process 2). A hardened product is taken out from the die (process 3) and heated inside a drying furnace and the resin component is vaporized and removed (process 4). A semiprocessed product in which metal particles are coarsely connected is sintered under a temperature near the melting point of a metal material and an end product provided with a prescribed dense composition is obtained (process 5). Though the semiprocessed product is slightly shrunk in the process of sintering, the shrinking rate is decided by a working condition and deformation is small. These conditions are sufficiently studied before mass production.