PURPOSE: To enable transmission of high frequency signal having less cross-talk by covering a periphery of a signal conductor with an electromagnetic shielding conductor and an electromagnetic shielding metal column body.

CONSTITUTION: A signal transmission conductor 4 is formed on both surfaces of a circuit board 1. An insulator 5 including its side wall is coated with an electromagnetic shielding conductor 6 entirely and uniformly. An electromagnetic shielding metal column body 7 consists of a highly conductive metal such as copper, and electrically insulated and positioned at an area near a side wall of the conductor 4. One end of the metal column 7 is electrically connected to a ground layer 2 inside the board 1, and the other end is electrically connected to the conductor 6. Adverse effects upon other signal conductors can be eliminated by covering a periphery of the conductor 4 with the conductor 6 and the metal column body 7 in this way. Transmission of high frequency signal having less cross-talk can be thereby realized.