PURPOSE: To realize a high response control by calculating the duration of maximum acceleration and deceleration and then shortening the time to be elapsed before a state of target speed and phase is reached.

CONSTITUTION: A reference signal is inputted under a state where a cylinder 2 is rotating at a target speed and a phase error detection circuit 6 determines a phase error θE based on a position detection signal generated from a position detection signal generator 4 and the phase error θE is fed to a control time calculation circuit 101. The control time calculation circuit 101 increases the difference between the rotational speed of a rotator and a target speed as large as possible and calculates maximum acceleration and deceleration times TP, TN, where the relative speed for making a transition to the target speed is increased, which are then delivered to a rotation command circuit 102. The rotation command circuit 102 outputs a maximum acceleration command to a cylinder drive circuit 8 only during the acceleration time TP being fed and accelerates a cylinder 2 to the maximum. Upon finishing output of maximum acceleration command, the rotation command circuit 102 outputs a maximum deceleration command only during the deceleration time TE and decelerates the cylinder 2 to the maximum thus shortening the time required for pulling in the phase.