It is proposed that three-dimensional integrated optics make it possible to integrate various optical devices which are made of materials peculiar to their function. In a preliminary experiment, an optical printed circuit board has been fabricated with an Si substrate. The output light was taken out at an angle of 57.5 degrees upward from the surface of the substrate, and the propagation loss was 2.8 dB when the waveguide was 4.43 mm long.