An image forming apparatus operable in a duplex print mode includes an image carrier and an image transferring device including a first and a second intermediate image transfer body whose surfaces are movable in contact with each other while forming a nip therebetween. Toner images are respectively transferred to opposite surfaces of a sheet using two pairs of conductive rollers that face each other via the first and second intermediate image transfer bodies at a nip. Two of the conductive rollers associated with the second intermediate image transfer body are transfer rollers respectively applied with one and the other of biases of opposite polarities.