To provide an image forming apparatus which can correct variations in the quantity of light from each LED element without the use of a separate sensor for reading the quantity of light generated from an LED print head, and an output data correcting method for the print head.

This image forming apparatus is equipped with the LED print head 62, a data conversion means 202 for converting data into output data to the print head 62 in accordance with pixel data of an output image, and a drive circuit 62b for driving an LED array 62a according to the output data acquired by the means 202. The image forming apparatus comprises an image output part which outputs an evaluation image by driving the print head 62 in accordance with predetermined evaluation data 204, an image reading part for reading the evaluation image which is output by the image output part 3, and a correction means 205 for correcting table data 206 for correction in accordance with the image data which are read out by the image reading part.