To prevent the occurrence of undesired toner scattering by changing the developing capacity of a developing means and the output of a transfer means to prescribed values during the interruption of forming an image.

As for a photoreceptor drum 38 whose toner image is already delivered to a paper, a charge and the toner remaining on the surface of the drum 38 are removed by a cleaning discharging device 48, thereafter, the drum is used for forming the image again. And in a period after the toner image is transferred to the paper until the next image is formed, the rotating speed of the developing roller 44a of the developing device 44 and the bias voltage impressed on a transfer guide plate 59 are reduced lower than respective normal values. Simultaneously, a developing bias voltage impressed on the developing device 44 is increased higher than the normal value. Thus, at the time of not forming an image, that is, in the case the paper does not exist in a transfer area, the amount of toner scattering in accordance with the rotation of the developing roller 44a of the developing device 44 and the amount of the suspended toner in the device due to the bias voltage of the transfer guide plate 59 are reduced, and soiling inside the device, or paper soiling, etc., by the toner attracted to the transfer guide plate 59 are reduced.