A pulse width modulation signal generating device which generates a pulse width modulation signal for modulating laser beam according to image data includes: a cycle signal output circuit which outputs a cycle signal having a cycle corresponding to a drawing rate for drawing the image data by the laser beam; and a pulse width modulation circuit which receives supply of the image data and the cycle signal and modulates a pulse wave having a cycle determined by the cycle signal by changing duty ratio of the pulse wave based on the image data to produce the pulse width modulation signal.