PURPOSE: To reduce causes of paper jamming, etc., and to reduce ozone quantity generated by corona discharge by variably controlling separating current according to the type of transfer medium utilized.

CONSTITUTION: A means to detect and discriminate the type of the fed transfer medium and generate a transfer medium type signal, and a means to control the feeding energy necessary to carry out separation with a separating means by the transfer medium type signal are provided. That is, before the image forming action is started, the type of the transfer medium 8 to be utilized is discriminated by the transfer medium type discriminating mechanism 11 and the medium type signal S1 is transmitted to the separating current value deciding mechanism 12. The selection and decision of appropriate separating current values against each transfer medium of various types decided beforehand is carried out by the separating current value deciding mechanism 12 which received the medium type signal S1, and the separating current value signal S2 is transmitted against the separating current generating mechanism 13. Thus, causes of paper jamming, etc., are reduced, and the ozone quantity generated by corona discharging is reduced.