To provide a light source device for an endoscope permitting to properly adjust a light quantity of illumination light supplied to the endoscope and obtain an image of proper brightness.

A histogram processing circuit 23 of a light device for an endoscope distributes luminance signals of each pixel of an image photographed by the endoscope 10 to either of the steps of the predetermined numbers, and obtains the number of luminance signals belonging to each step as histogram data. And, a comparison value specifying part 24 totals the number of luminance signals belonging to each step from the highest step to the subordinate position based on the histogram data, and specifies the brightness of the step as the comparison value when this total value arrives at the specified value. A CPU (comparison part) 24 compares the comparison value with a reference value, and controls a light quantity adjusting part 3 to decrease the light quantity of the illumination light supplied to the endoscope 10 when the comparison value exceeds the reference value, and to increase the light quantity of the illumination light supplied to the endoscope 10 when the comparison value is below the reference value.