To prevent or reduce the wear of the surfaces of an image forming body and an intermediate transfer body by moving a bias transfer roll in such timing that the speed differen between the image forming body and the intermediate transfer body is caused.

For example, a digital color copying device is constituted so that a supporting member 28 freely rotatably supporting the bias transfer roll 6 press-contacting with a photoreceptor drum 1 is supported from the lower part by a tie plate 30 through a tension spring 29. The supporting member 28 is made in press contact with an eccentric cam 33 by the spring 29 so that it can be moved up and down by the rotation of the cam 33. Then, the roll 6 is moved in a direction where it is away from an abutting position of the drum 1 and an intermediate transfer belt 5 in such timing that the speed differen is caused at the time of starting between the drum 1 and the belt 5 at the first and the last or falling the device and at the time of traveling a special paper.