An electronic circuit board having an optical wiring layer sandwiched between two electrical wiring layers. The optical wiring layer is structured to be a two-dimensional optical waveguide. An E/O device and an O/E device are provided in the optical wiring layer or at an interface between the optical wiring layer and the electrical wiring layer. A via piercing the optical wiring layer connects the two electrical wiring layers. It is possible to efficiently input and output light to and from an optical wiring layer.