PURPOSE: To prevent plastic from leaking onto a wire netting and at the same time contrive to reduce the deformation of the wire netting by a method wherein metal wires consisting the wire netting are flattened at the part near a frame.

CONSTITUTION: The end part of a wire netting 2 is pressingly held by lands 10 and 10', which are respectively provided on an A-mold 6 and on a B-mold 7 under the state that the wire netting 2 is housed in a cavity 11, which is provided at the central part of the molds. The interval between the lands 10 and 10' corresponds to the thickness B of the compressed wire netting, under the state wherein neither clogging of the netting nor extreme lowering of the strength at the compressed part of the netting will occur. In addition, at the cavity 11, the wire netting and the mold 5 do not touch with each other. After the mold 5 is assembled as mentioned above, synthetic resin is forced from a runner 8 in the mold 5 so as to mold the frame 3 of an oil filter 1. After cooling, the molded frame is taken out by disassembling the mold. Since the wire netting is pressingly pinched by the lands, leakage of the molten synthetic resin from the cavity 9, which forms the frame, of the mold through the mesh of the wire netting does not occur into the cavity 11, in which the wire netting is inserted, further development of flash or partial clogging of the wire netting does not occur.