An automatic document feeder used in a facsimile machine, photocopier or the like. The DC component of a load torque is derived from the sum of absolute values of a torque applied to a link connected to the output shaft of a motor and the generated torque of the motor, and it is determined that overload has been applied when the DC component exceeds a first threshold value for a prescribed period of time or longer. After that, the nominal fuel quantity is modified according to the value of the at least one first parameter so as to obtain a corrected fuel quantity that corresponds to the actual fuel quantity injected during the injection.