An image forming apparatus in which a BD signal, which is a main-scanning reference signal, and image data are input to an image signal generating unit. Using a converting unit, main-scanning coordinate information, output from a main scanning coordinate measuring counter, and correction amounts, recorded in a correction amount LUT, are referred to, to convert a proper amount of image data. Here, the converting unit performs calculations in accordance with the main-scanning coordinate information, to obtain the image data of correction amounts that differ in accordance with coordinates. The correction amounts are in correspondence with different amounts of driving current in a main-scanning direction. Therefore, laser light emission, which provides a light quantity in accordance with the image data, is controlled.