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 including an optical fiber for guiding excitation light emitted from a light source； a first mirror and a second mirror disposed facing a light emission end at a distal end of the optical fiber and diffusing the excitation light emitted from the light emission end； and a phosphor on which the excitation light diffused by the first mirror and the second mirror is incident and which emits fluorescence.
