PROBLEM TO BE SOLVED: To provide a light source device for an endoscope, a method for controlling light intensity of the same and an endoscope system, wherein a ratio between white illumination light and narrowband light is uniformly maintained in special light observation to maintain a light intensity balance or a color balance of two sides, and wherein a high-accuracy special light observation image not having a change or having a small change in brightness or a hue can be obtained, so that high-accuracy observation image wherein the whole image is bright can be obtained when performing the special light observation and normal observation to allow high-level diagnosis.SOLUTION: This light source device for the endoscope includes: a wave-combining member having a transmission part which transmits the white illumination light emitted from a first light source part and a reflection part which reflects at least the narrowband light emitted from a second light source part, and generating wave-combined light by combining waves of the white illumination light and the narrowband light a light intensity measurement means measuring light intensity of the wave-combined light and a light intensity control means controlling a drive part of the second light source part such that light intensity of the narrowband light is adjusted according to the measured light intensity of the wave-combined light.
