A light source device includes a light source 8, a diaphragm blade 21 for adjusting light quantity of illumination light supplied from the light source 8, a diaphragm driving part 25 for driving the diaphragm blade 21 to perform opening/closing operation, and a diaphragm control circuit part 23 for setting diaphragm drive instruction voltage to be supplied to the diaphragm driving part 25 and control an opening/closing amount of the diaphragm blade 21. In the diaphragm control circuit part 23, a fully-opened voltage and a fully-closed voltage at the time the diaphragm blade 21 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 21 is set, and based on the adjustment data, a control range of the diaphragm drive instruction voltage is regulated.
