PURPOSE: To obtain an image without uneven density by providing two control means which control driving of a driving means and constituting the 2nd control means thereof in such a way as to select the output time of the control signal patterned preliminarily according to the detection output.

CONSTITUTION: A motor driver controller 10 monitors the rate of phase deviation (rate of change) within the prescribed time detected by a differentiating and detecting circuit 9 and outputs a control signla C1 to a motor driver 8 when the said rate of change is of a certain set value or above. The driver 8 is changed over from a contact point S2 to S1 when the signla C1 is outputted. A saw tooth wave is applied to the minus terminal of the comparator COMD in the driver 8 and since a DC voltage is impressed from the contact point S1 or S2 to the plus terminal and therefore the pulse width of the pulse P inputted to a motor 1 is controlled by the magnitude of the DC voltage to be impressed to the plus terminal.