An image forming method includes rotating a transfer roller which forms a transfer nip by coming in contact with a transfer belt and has a concaved portion wider than the transfer nip in a rotation direction, such that the concaved portion comes to a position of facing the transfer belt, stopping rotation of the transfer roller at a position where the transfer belt faces the concaved portion of the transfer roller and the transfer belt and the transfer roller are spaced apart from each other, moving the transfer belt while the transfer roller is stopped and transferring an image formed on an image carrier to the transfer belt, and detecting the transferred image by a detection portion.