An image forming apparatus capable of correcting light amounts of light beams which expose a photosensitive member with simple construction. The image forming apparatus includes a photosensitive drum, and a beam scanning device including a plurality of semiconductor lasers which emit light beams for exposing the photosensitive drum, and a memory which stores first correction data for correcting the light amount of each light beam in a manner associated with each of the plurality of semiconductor lasers. A CPU outputs second correction data for being commonly used in correcting the light amounts of the light beams emitted from the plurality of semiconductor lasers to the beam scanning device. A laser driver IC provided in the beam scanning device controls the light amount of the light beam emitted from each semiconductor laser based on the first correction data and the second correction data.