PROBLEM TO BE SOLVED: To provide an endoscope system, a light source device, an operation method for the endoscope system, and an operation method for the light source device capable of guaranteeing the maximum quantity of illumination light even if the light emission quantity of the light source is limited by the radiation performance of the radiation mechanism or the power capacity of the power source.SOLUTION: The endoscope system 10 comprises: a first emission unit for emitting green narrow-band light Gn a second emission unit for emitting blue narrow-band light Bn a light source control unit 25 for controlling the first emission unit and second emission unit to apply the first light, second light, or both the first light and second light onto an observation object and an imaging sensor 48 for imaging return light from the observation object. The light source control unit 25 provides for a first light irradiation period during which the first light is applied onto the observation object, a second light irradiation period during which the second light is applied onto the observation object, and a superposition irradiation period during which both the first light and second light are applied onto the observation object by a different light quantity ratio from the light quantity ratio between the first light during the first light irradiation period and the second light during the second irradiation period.SELECTED DRAWING: Figure 2
