In this embodiment, soft plastic films 51 and 52 made for example of nylon, polyester, polyurethane, polyimide or polyfreon are respectively adhered to the inner walls 21a and 21b and the step portions 26 and 27 of the housing 2 to provide the required soft waterproof layers for enclosing the first magnetic path connection end faces 31 and 32 of the first laminated cores 3 which are respectively e