Abstract: An “interval” in which the synchronization status between the movable axes subject to synchronous control is monitored, an equation between the movable axes in the “interval”, and an “allowable displacement” for the positional relationship obtained with this equation and the actual positional relationship are set in advance. The “start condition” and “termination condition” for synchronous status verification processing are set with the master position and the like. When the start condition for synchronous status verification processing is satisfied, it is detected whether or not the actual position and the position obtained with the equation are within the range of the allowable displacement based on the position of the movable axes. If not within the range of the allowable displacement, operation set as “operation to be executed when the allowable displacement is exceeded” is executed.