In order to avoid a frequent multiple crossing in an optical fiber in a sheet and attach the optical connector near a marginal end of the sheet while maintaining a sufficient extra length and more extra length for attaching the optical fibers, in the optical fiber sheet 6, an optical fiber 5 as an extra length section in the optical fiber path is disposed on three-layer wiring planes which are formed by attaching four sheets 1, 2, 3, and 4. Notched sections 2a and 3a are formed in the intermediate layers 2 and 3. The optical fiber 5 communicates from a first wiring layer to a second wiring layer via the notched section 2a so as to communicate from the second wiring layer to a third wiring layer via the notched section 3a.