A high-frequency clock generating circuit generates a plurality of high-frequency clock signals having different phases. A modulation-signal generating circuit generates a pulse modulation signal based on transition timing data including data pertaining to a turn-on timing at which a state of a light source is changed from a turn-off state to a turn-on state and a turn-off timing at which the state of the light source is changed from the turn-on state to the turn-off state by inputting any one of the high-frequency clock signals for a predetermined period including the turn-on timing and the turn-off timing.