PURPOSE: First to form the interior of a driven magnet, and a central bearing hole by means of resin molding, with high digree of concentricity of driven magnet, and subsequently support the magnet on the basis of said bearing hole by a mold so that a uniformly thin resin layer may be formed on the outer periphery of the driven magnet.

CONSTITUTION: In the process of forming a pump runner 19, the whole surface of the outer periphery of an annular driven magnet 16 processed in a perfectly round form of its outer periphery as shown in a drawing and the surface of the inner periphery of a bearing sleeve 17 are supported by a mold as a standard surfaces so as to form the first resin molding in a solid line area, and thus semifinished runner 19 is obtained. Thereby, the outer periphery surface of the driven magnet 16 has high degree of concentricity in relation to the inner periphery surface of the bearing sleeve 17. Later, resin molding of the runner 19 is completed through supporting the inner periphery surface of the bearing sleeve 17 by a mold and forming the second resin molding in an area in a dashed line. By this method, a uniformly thin layer of resin without any joint may be formed on the outer periphery surface of the driven magnet 16.