An object of this invention to transfer the light emitted from the light source and exit the light with a uniform distribution of light quantity, without incurring transfer loss and an increase of costs.In this invention, an optical fiber 11 for irradiation-light transfer of a single major optical fiber element composed of a core 12 and a clad 13 is bent in its intermediate region in an annular shape to form an annular portion 14. The crossing zone at the annular portion is fixed by a fixing member 15. By incidenting light from its incidence terminal 11a, variations in the distribution of light quantity are eliminated at the annular portion 14 so that the light with distribution of light made uniform is exited from an exit terminal 11b.