Disclosed is a composite optical fiber which has high flexibility and is hard to break. The composite optical fiber comprises a larger-diameter optical fiber and smaller-diameter optical fibers each having a smaller diameter than that of the larger-diameter optical fiber, wherein the larger-diameter fiber and the smaller-diameter optical fibers are so arranged that the larger-diameter fiber is surrounded by the smaller-diameter optical fibers, and the smaller-diameter optical fibers that surround the larger-diameter optical fiber are made from a plastic material.
