A light source device includes a xenon lamp, a rotary shutter, a main CPU for controlling drive of these components, and a sub CPU. The main CPU operates when receiving a reset cancel signal from a reset circuit. Between the sub CPU and the reset circuit, an AND circuit is provided. When the reset cancel signal from the reset circuit and a lighting completion signal indicating completion of lighting the xenon lamp are both input, the AND circuit outputs the reset cancel signal to the sub CPU. After the output of the lighting completion signal, the sub CPU operates to drive the rotary shutter. When high-frequency noise which occurs at the time of discharging the xenon lamp stops, the rotary shutter is activated and thereby generating pulses of illumination light.