PURPOSE: To eliminate the need for a shield plate and to reduce the operation man-hours and package space by forming a shield structure by using through holes.

CONSTITUTION: Transmission lines consist of a ground surface 10 and signal lines and the through holes 13 are connected electrically to the ground surface 10 to separate the respective lines as to high frequencies. Namely, the through holes 13 which are arranged at short pitch serve as the cutoff rod of a waveguide and cut off electromagnetic waves below a certain frequency to provide the same effect with the arrangement of a shield plate. Thus, the shield structure is formed by using the through holes 13, so the need for the shield plate is eliminated and the operation man-hours and package space are reduced.