To provide a differential signal line which can adjust an electric length of a differential wiring, without increasing the area required for wiring and requiring a special substrate structure in a via connecting the differential signal lines, through a plurality of signal layers of a multi-layer printed substrate.

In a via pair (2a, 2b) connecting differential signal transmission routes (1a, 1b; 3a, 3b) over a plurality of signal layers of the multi-layers printed substrate, a cross section shape of at least one side of a via pair is circular, and the other cross section shape is elliptical.