To control a rotational drive source to be at a specified rotational speed, and also, transmit the rotation to the target of control through a reduction gear and a transmission means without rotational irregularity, other kinetic irregularity, etc., and besides stably and with high accuracy, and besides, contrive downsizing.

This controller is so arranged as to control a DC motor 9 so that the rotational speed may synchronize with a row of reference pulses and also to transmit the rotation of the target 14 of control through a reduction gear 12 and a transmission means 13, and this is equipped with a rotary encoder 11 which detects the rotational speed, being provided at the rotary shaft of the DC motor 9, a phase sensor 17 which detects the motion, being provided at the mobile part of the control target 14, a frequency difference detector 4 which detects the frequency difference between the row of speed pulses outputted from the rotary encoder 11 and a row of reference pulses, and an output varying means 5 which increases and decreases the rotational speed of the DC motor 9, based on the frequency difference and the phase difference.