PURPOSE: To eliminate the erasion of an image already color-tone processed and to prevent interaction by providing a means for controlling the interval of the cloud of material particles for an image receiving body without strongly performing interaction with an image receiving surface.

CONSTITUTION: AC/DC voltage is impressed between a donor base substance which is color-toned and a wire rod 48 automatically coming in contact with a donor roll 42 which is color-toned by leaving a fixed distance, and another AC/DC voltage is impressed between a donor roll/wire rod electrode assembly and ground. The level of the AC/DC voltage between the donor and the wire rod electrode is set to an optimum value for the separation of toner and the formation of the toner cloud, on the other hand, the level of the AC/DC voltage between the donor and the image receiving body is set to the optimum value for the control of the position of the toner cloud in the void of a developing device. Therefore, double AC voltage constitution is the optimum performance of the device. Thus, the line image is excellently devoloped by the AC/DC voltage to control the toner cloud in the void of the developing device, and the interaction between the toner and the image receiving body becomes minimum.