120 due to attraction toward the permanent magnet 140 in the bobbin 111 although not shown in the drawings the moving part 130 is elastically biased away from the permanent magnet 140 by an elastic member such as a spring in the above structure when no current is supplied to the coil section 110 the moving part 130 makes contact with the frame 120 due to the attraction of the permanent magnet 140 when current is supplied to the coil section 110 the moving part experiences a magnetic force that counteracts that of the permanent magnet 140 then the restoration force of the elastic member not shown causes the moving part 130 to detach from the frame 120 the frame 120 and the moving part 130 are made of ordinary steel because steel is corroded by moisture or salt the surface of the frame 120 and the moving part 130 are plated with anti corrosion material to prevent corrosion anti corrosion materials are nonferrous and have a diamagnetic composition such as nickel or copper and nickel in order to provide effective prevention against corrosion it is necessary for the plating to have a certain thickness for example if nickel or copper and nickel is used as the anti corrosion material the required thickness of the plating is more than 7 u03bcm however in this case the force of adhesion between the moving part 130 and the frame 120 can be decreased by the anti corrosion material a contact surface 132 of the moving part 130 accounts for only a very small portion of the total surface area of the moving part 130 and likewise for a contact surface 123 of the frame 120 hence it is unlikely for the.