A common insulating plate 16 is prepared such that a plurality of paired upper and lower electric wire fitting grooves 16b and 16d are formed straight in the insulating plate 16 at a constant pitch P1 in the transverse direction, and such that a plurality of press-fitting slits 16e are formed in the individual electric wire fitting grooves 16a and 16c at a constant pitch P2 in the longitudinal direction; compression relay terminals 17 are press-fitted in suitable positions of the individual press-fitting slits 16e: and the electric wires 15 are individually fitted in the paired upper and lower electric wire fitting grooves 16b and 16d having the compression relay terminals 17 press-fitted therein, so that the upper and lower electric wires 15 are individually compressed and connected in the upper and lower compression blades 17a and 17b of the compression relay terminals 17 so that the upper and lower electric wires 15 of the insulating plate 16 can be electrically connected.