A manufacturing method has a process for arranging N-1 pieces of conveyance molds (10) between coil parts (111) which are coaxially arranged for N stages (N is integer of 3 or above) and for radially orienting magnetic powder in the conveyance molds (10) with an opposed magnetic field generated from the adjacent coil parts (111), a process for pressurizing magnetic powder in the conveyance molds (10), a process for demolding an oriented and pressurized ring compact from the conveyance mold (10) and laminating a plurality of the ring compacts and a process for sintering and integrating the laminated ring compacts. The coil parts (111) generate an AC magnetic field whose amplitude attenuates with time.