A differential signal pair transmission structure adapted to a wiring board and including a first signal path and a second signal path is provided. The first signal path includes a first upper trace, a first lower trace and a first conductive through via. The second signal path includes a second upper trace, a second lower trace and a second conductive through via. A portion of the first signal path and a portion of the second signal path overlaps in the normal projection onto the upper or lower surface of the wiring board. Normal projections of the first and the second signal path projecting onto the upper surface of the wiring board are substantially symmetric with respect to a line which is perpendicular to a segment connecting normal projections of axes of the first and the second through via onto the upper surface and passes through the midpoint of the segment.