PURPOSE: To obtain highly accurate synchronization characteristics by adding the deviation of each actuator to the average values of the displacement, velocity, and acceleration of all actuators in the feedback systems of a plurality of actuators provided along one driving direction of a vibration tester.

CONSTITUTION: Adders 15aW15d are provided in feedback systems of displacements of actuators 4aW4d, respectively. Adders 16aW16d and bypass-filter and limiter circuits 17aW17d are provided in feedback systems of velocity and acceleration from the actuators 4aW4d. The displacement deviation is applied to the adders 15aW15d from a synchronization-control-signal calculator 19, and the velocity deviation and acceleration deviation are added to the adders 16aW16d, thereby the feedback is accomplished.