An image forming apparatus includes a profile storage section that stores distortion characteristic of a scanning line, a correcting section that corrects image data by lines in the sub scanning direction, and a registration sensor that detects a pattern image for detecting color misregistration amounts in a sub scanning direction of images formed on an intermediate transfer member. When the pattern image is formed, the distortion correcting section shifts image data of the pattern image by lines in the sub scanning direction so that, with reference to a detection position of the registration sensor, a positional displacement amount of the pattern image in the sub scanning direction becomes less than or equal to ½ of a scanning-line distance, in accordance with a positional displacement amount of the scanning line in the sub scanning direction at a detection position of the registration sensor along a main scanning direction.