TRANSFER METHOD

PURPOSE:To obtain a copy image of good quality by applying a DC voltage to a corotron at low humidity and applying a DC pulse voltage to the corotron at high humidity. CONSTITUTION:The transfer corotron 7 is connected to a DC voltage source 11 and a pulse voltage power source 12 through a changeover switch 10, which is connected to a humidity sensor 14 through a control circuit 13. The control circuit 13 compares the output of the humidity sensor 14 with a reference value of humidity and changes contacts of the switch 10. Namely, the changeover switch 10 is switched to the DC voltage source 12 when the humidity is not high and to the pulse voltage source 13 at high humidity. Thus, the DC voltage is applied to the transfer corotron 7 at normal or low humidity and the DC pulse voltage to the transfer corotron 7 at high humidity, so that the resistance of a transfer sheet 6 does not decreases at the normal or low humidity. Consequently, an excellent copy is taken over a wide environmental condition range.