An image forming apparatus is provided. The image forming apparatus includes a moving body which moves in a moving direction; a plurality of formation units which are provided to oppose the moving body, respectively, and align in an alignment direction, and which sequentially form images directly on the moving body or an image forming medium transported on the moving body; a detection section which outputs a detection signal corresponding to a position of a mark which is formed directly on the moving body or the image forming medium by each of the formation units; and a measurement section which specifies a positional relationship between marks formed by at least two formation units based on the detection signal from the detection section, and which measures a deviation angle between the moving direction of the moving body and the alignment direction of the formation units based on the specified positional relationship.