PURPOSE: To provide a printed wiring board where measures against EMI is fully considered from the design stage and the addition of a screening cover and parts against EMI is suppressed greatly.

CONSTITUTION: Conductor layers 1 and 2 with at least both front and rear surfaces consist of a power supply circuit 11 and a grounding pattern 12 which become a grounding level in terms of high frequency, a main circuit and the other circuit pattern 31 are formed in an inner conductor layer 3 and are connected to surface-mount parts 4 or the power supply circuit 11 and the grounding pattern 12 through a via 5 or a through hole 55 and further the through hole 55 is densely provided along the peripheral edge with a minimum lattice pitch P and then the conductor layers 1 and 2 on both front and rear surfaces are connected in continuity.