An image forming apparatus includes a first registration mark detection unit, second registration mark detection unit, CPU, and first registration mark time difference storage. If the width (tp) of the first registration mark signal detected by the second registration mark detection unit is equal to or smaller than a set value, the CPU directly uses, as an enable signal for controlling paper conveyance, the first registration mark detection signal detected by the first registration mark detection unit. If the width (tp') of the first registration mark signal detected by the second registration mark detection unit is equal to or larger than a set value, the CPU controls a paper conveyer by setting, as a correct first registration mark position, a position shifted by tE measured from an error signal, from the first registration mark detection signal detected by the first registration mark detection unit.