This endoscope system has: an insertion unit; an optical transmission unit provided to the insertion unit, for transmitting illuminating light impinging on the basal end to the distal end; a light source unit for producing light of a first wavelength band and light of a second wavelength band; a first lens unit into which light of the first wavelength band and light of the second wavelength band from the light source unit enters, and from which light exits having spatial intensity distribution characteristics that differ according to wavelength; a second lens unit facing the first lens unit, for directing light exiting from the first lens unit to enter the basal end of the optical transmission unit; a distance adjustment unit for adjusting the distance between the first lens unit and the second lens unit; and a controller for controlling the distance between the first lens unit and the second lens unit in such a way that the quantity of light of the first wavelength band and the quantity of light of the second wavelength band exiting from the distal end of the optical transmission unit are brought to a prescribed quantity of light ratio.