In fabricating an optical I/O array module, an optical waveguide provided with mirror parts, each having a tapered face, is formed on a substrate, a convex shaped member or a concave shaped member is placed at spots above the respective mirror parts of the optical waveguide, and laser diode arrays and photo diode arrays, provided with either a concave shape, or a convex shape, are mated with, or into the convex shaped member or the concave shaped member before being mounted. Further, there are formed multiple filmy layers, on which an LSI where a driver IC LSI of optical elements, and an amplifier LSI of the optical elements are integrated.