An image forming apparatus that forms an image using a plurality photoconductor bodies includes a cleanerless transfer belt configured to convey paper to the plurality of photoconductor bodies and a switching unit configured to switch on/off a cleaner for each of the photoconductor bodies, on the basis of whether a single mono-colored developing agent is adhered to the transfer belt or whether two or more mono-colored developing agents are adhered to the transfer belt. A control unit is configured to control a change of a transfer bias for each of the photoconductor bodies, when the switching unit switches on/off the cleaners.