A light source apparatus irradiates an observation target with first light in a wavelength region which does not include a wavelength region where an absorption peak of a target substance included in the observation target is present and second light in a wavelength region where the absorption peak is present. An image acquiring circuit includes an emphasized image information generating circuit which generates emphasized image information on the basis of first image information acquired by an imaging apparatus when the observation target is irradiated with the first light and second image information acquired by the imaging apparatus when the observation target is irradiated with the second light.