A misregistration amount detector in a tandem image forming apparatus having a conveying body configured to convey paper on which a color image is to be printed is disclosed. The misregistration amount detector includes an image creating part configured to create, on the conveying body, a first pattern for detecting the amount of misregistration of an image position related to a first color relative to an image position related to a second color other than the first color and a second pattern for measuring the conveyance speed of the conveying body, the first pattern and the second pattern being side by side in the conveyance direction of the conveying body, and a reading part configured to read the first pattern and the second pattern created on the conveying body by the image creating part.