An endoscope light source unit for making illumination light incident on a light guide, includes a rotary aperture plate, aperture openings of different opening ratios and an auxiliary-light aperture opening of a maximum opening ratio formed in the rotary aperture plate a rotating device an auxiliary light a first sensing portion and a plurality of second sensing portions formed in the rotary aperture plate in association with the auxiliary-light aperture opening and the aperture openings a first sensor which detects the first sensing portion a second sensor which detects the first sensing portion and detects the second sensing portions and a controller which controls the rotary aperture plate in accordance with the first and/or second sensors. When the auxiliary light is in the retracted position, the controller drives the rotary aperture plate while the second sensor detects the first sensing portion.
