PROBLEM TO BE SOLVED: To provide a light source device for endoscope, an endoscope system, and their operation methods in which, in a special light observation, a ratio between white illumination light and narrowband light can be kept constant, the light amount balance and color balance between them can be maintained, a high-definition special light observation image with no or little change in brightness and hue can be obtained, and, as a result, a high-definition observation image bright as a whole can be obtained in special light observation and normal observation and a high level of diagnosis becomes possible.SOLUTION: A light source device for endoscope comprises: light quantity measuring means for measuring the light quantity of multiplexed light in which white illumination light emitted from a first light source part 24 and narrowband light emitted from a second light source part 26 are multiplexed and light quantity control means for controlling a drive part 42a of the second light source part 26 to adjust the light quantity of the narrowband light according to the measured light quantity of the multiplexed light.
