PURPOSE: To eliminate useless time in terms of paper feeding and to accelerate a transfer by equalizing the paper feed timing from a paper feed cassette so as to wait in the position of a resist roller, and transferring and feeding paper at the timing in response to an action mode.

CONSTITUTION: Normally the transfer action is executed in a 1st action mode. A detection light 19 scans an original in a fixed area between positions P3 and P4 to detect the density of the original, and a development bias voltage is controlled accordingly. If an original detection signal in the section between P3 and P4 is beyond a preset range, the 1st action mode is switched to a 2nd action mode, and the area in which the density of the original is detected is extended to control the voltage. Even in the 2nd action mode a transfer sheet 3 is fed from the paper feed cassette in the same way as in the 1st action mode. If the transfer sheet 1 stops on the resist roller 14, it is put on standby. When the transfer action is executed in the 2nd action mode, the transfer sheet 13 on standby is fed at the timing in response to the roller 14, whereby the useless time in terms of paper feeding can be eliminated.