A flexible optical substrate allows incident light or optical signals to be propagated or transmitted the flexible optical substrate. The flexible optical substrate includes unitary elastic structures. Each of the unitary elastic structures includes a film-like resin material that has a central portion and one or more strips provided outwardly of the central portion. One end of each of the one or more strips is connected to the central portion. Each of the unitary elastic structures has a clearance. Two adjacent unitary elastic structures are linked by at least part of the strips of the two adjacent unitary elastic structures.