An image forming apparatus includes a recording medium transport belt which is suspended by a plurality of roller members. An image is secondarily transferred from a first image carrier through an intermediate transfer body to a recording medium. An image is directly transferred from a second image carrier to the recording medium. The image forming apparatus further includes a pattern image sensing unit which senses a pattern image transferred from the first image carrier and the second image carrier finally to the recording medium transport belt. Each of a distance from a secondary transfer position to a sensing position and a distance from a direct transfer position to the sensing position in a recording medium transport belt rotation direction is a natural number times a circumferential length of a roller member causing a speed change in the recording medium transport belt among the plurality of roller members.
