To improve reliability of signal transmission of an interposer which couples between semiconductor chips. A reference potential wiring and a reference potential wiring are provided on both neighboring sides of a signal wiring provided in a first wiring layer of an interposer. Also, a reference potential wiring and a reference potential wiring are provided on both neighboring sides of a signal wiring provided in a second wiring layer of the interposer. Further, the signal wiring and the signal wiring cross each other in plan view. The reference potential wirings of the first wiring layer, and the reference potential wirings of the second wiring layer are coupled to each other at the periphery of their crossing portion.