A shield conductor Wa comprises: a metallic pipe 20, a wire 10 to be inserted into the pipe 20, and a groove-like fitting member 22 provided in the pipe 20 as extending along the direction of axis of the wire 10, and at the same time, attached tightly to the circumference of the wire. One or more contacts of the user associated with the authentication request are determined. The respective clocks are variably delayed based on the comparison result so as to allow the device additionally installed to perform clock phase control as to the work and protection lines.