A wide range is illuminated with a sufficient light amount while a diameter of an insertion portion is reduced. Provided is an illumination optical system for endoscope (1) including an optical fiber (6) for guiding excitation light emitted from a light source； a first mirror (9) and a second mirror (10) disposed facing a light emission end (6a) at a distal end of the optical fiber (6) and diffusing the excitation light emitted from the light emission end (6a)； and a phosphor (11) on which the excitation light diffused by the first mirror (9) and the second mirror (10) is incident and which emits fluorescence.
