A light source device includes a light source, a diaphragm blade for adjusting light quantity of illumination light supplied from the light source, a diaphragm driving part for driving the diaphragm blade to perform opening/closing operation, and a diaphragm control circuit part for setting diaphragm drive instruction voltage to be supplied to the diaphragm driving part and control an opening/closing amount of the diaphragm blade. In the diaphragm control circuit part, a fully-opened voltage and a fully-closed voltage at the time the diaphragm blade is fixed at a fully-opened position and a fully-closed position are read, based on the voltages, adjustment data for adjusting the diaphragm drive instruction voltage and the opening/closing positions of the diaphragm blade is set, and based on the adjustment data, a control range of the diaphragm drive instruction voltage is regulated.
