To provide a printed wiring board which enables a high density wiring of wiring patterns without degrading the signal transmission quality due to a crosstalk noise.

A ground pattern 6 is formed between a pair of strip lines 4 and a ground layer 1b, while a ground pattern 7 is formed between a pair of strip lines 5 and a ground layer 1a. Due to this structure, the expansion of an electromagnetic field from the strip lines 4a and 4b toward the ground pattern 1b and the expansion of an electromagnetic field from the strip lines 5a and 5b toward the ground pattern 1a can be suppressed by electromagnetic coupling between the ground patterns 6 and 7, resulting in suppressing crosstalk noise between pairs of strip lines 4 and 5. Thus, without adding a new interconnection layer, the degradation of signal transmission quality due to crosstalk noise can be eliminated and the strip lines 4a, 4b, 5a, and 5b can be wired at a high density.