A controller controlling a synchronized operation of spindle and feed axes. The controller is configured to make a spindle axis perform an accelerated rotation at maximum capacity from a starting position aiming at a maximum rotation speed; detect a maximum acceleration of the spindle axis; detect a residual rotation amount of the spindle axis; detect a current speed of the spindle axis; and execute a position control for making the spindle axis perform a decelerated rotation so as to reach a target position, after the accelerated rotation at maximum capacity. The controller is further configured to make the spindle axis perform the decelerated rotation at a positioning deceleration higher than a deceleration corresponding to the maximum acceleration and equal to or lower than a maximum deceleration capable of compensating for a mechanical loss in a drive source during the decelerated rotation of the spindle axis.