A device is provided that includes a core having a first end and a second end, and first and second wires wound around the core so as to cross each other on the core to form a cross point. The a winding structure of an ith turn of the first and second wires counting from the cross point toward the first end, and a winding structure of an ith turn of the first and second wires counting from the cross point toward the second end, are substantially symmetrical about the cross point.