Abstract: A light source drive controlling device for use in an image forming apparatus is provided for controlling a light source for illuminating a surface of a document wherein the light amount of the light source is adjusted in accordance with a level of drive voltage supplied thereto by a light source driving device for supplying a drive voltage of a specified level to the light source. A scanning mechanism for moving the light source to and from a home position and a return position whereat scanning is completed moves the light source through an image reading start position whereat scanning an image of the document begins. A drive voltage supply timing controller varies a drive voltage supply start timing for applying the drive voltage to the light source in accordance with the level of drive voltage such that the light amount of the light source reaches a predetermined level when the light source reaches the image reading start position.