IMAGE FORMING APPARATUS

An image forming apparatus which inhibits occurrence of defective image caused when buffer consumption amount in the sector correction exceeds a previously estimated capacity. The image forming apparatus comprises a line buffer for temporarily storing image data. The image forming apparatus performs correction processing to the image data to correct distortion of the image to store the corrected image data in the line buffer. Further, the image forming apparatus forms images on a recording medium based on the image data having experienced the correction processing. The CPU of the image forming apparatus determines whether a size of the image data having experienced the distortion correction by a first correction value based on the sector correction seed value exceeds the number of lines in the line buffer. If it is determined that it exceeds the number of lines, the CPU obtains a second correction value, in which the first value is corrected.