The present invention provides a lighting device capable of controlling finely modulated light control without stopping other processing regardless of an operation clock. The light modulation signal generating portion calculates a cycle of a PWM signal based on the lighting state of lamp, which is detected by state detecting portion and a predetermined operation clock. A PWM signal of the cycle calculated by the state detecting portion is generated by the light modulation signal generating portion capable of generating the PWM signal corresponding to the cycle of a non-integral number of times of the operation clock, wherein the cycle of the PWM signal can be continuously and finely varied without stopping other processing regardless of operation clocks, and fine modulated light control is enabled.