An observation system includes: a light source device capable of generating light of a plurality of wavelength bands different from each other, as illumination light for illuminating biological tissue； a light source control portion configured to control the light source device so as to generate the light of the plurality of wavelength bands at a predetermined light quantity ratio； an emphasizing processing portion configured to execute predetermined emphasizing processing for highlighting one or more structures included in the biological tissue based on a desired emphasis degree to an image obtained by picking up an image of return light from the biological tissue illuminated by the illumination light； and a control portion configured to output a light quantity ratio control signal for controlling a light quantity ratio of the light of at least two wavelength bands of the light of the plurality of wavelength bands to the light source control portion based on setting of the desired emphasis degree, and perform control for the emphasizing processing portion to perform the predetermined emphasizing processing.
