PURPOSE: To keep the transfer corona charge amount constant to uniformize electrification, and prevent irregular print density by controlling the discharge current of a transfer charger according to whether a transfer material is existing or not.

CONSTITUTION: In using a cut paper sheet as a transfer material 3, the existence or non-existence of the transfer material 3 between a transfer charger 1 and a photo-sensitive body 2 is transmitted as a report signal from a sheet travel detection section 5 to a control section 6. According to this report signal, the control section 6 regulates high voltage applied from a high voltage section 7 to a corona discharge electrode 4, thereby controlling corona discharge current. In other words, a normal transfer process takes place, when the transfer material 3 is existing between the transfer charger 1 and the photo-sensitive body 2. If the transfer material 3 is not existing, a discharge amount from the transfer charger 1 is controlled, according to a signal from the sheet travel detection section 5, thereby reducing a transfer corona charge amount to the photo-sensitive body 2. According to this construction, a transfer corona charge amount applied to the photo-sensitive body 2 can be kept constant, regardless of the existence or non-existence of the transfer material 3.