PROBLEM TO BE SOLVED: To provide a composite optical fiber which ensures sharpness of a subject image and can be miniaturized without degrading lighting capability and definition.SOLUTION: A hollow optical fiber includes cylindrical parts A, B, and C which are concentrically arranged and are connected into one body, and the cylindrical part A is located inside the cylindrical part B, and the cylindrical part C is located outside the cylindrical part B, and a refractive index a of the cylindrical part A, a refractive index b of the cylindrical part B, and a refractive index c of the cylindrical part C satisfy conditions a
