To constitute a feed back control system by using a value for detecting properties about the limited number of variables, and a calculating device for carrying out a simple calculation processing, and suppress vibration of a structure effectively.

A small cycle formed by dividing one operation cycle of an actuator 6 into a plurality of cycles is set to a cycle for detecting the properties of a structure 1, a feed back coefficient rated per time detected by those detecting cycles is multiplied by each property detecting value, and those linear sum is set as a manipulated variable command value of the actuator 6. Otherwise, a small cycle formed by dividing one detecting cycle of the property into a plurality of cycles is set to the operating cycle of the actuator 6, a feed back coefficient rated per time operated by those operating cycles is multiplied by the properties detecting value in the one detecting cycle, and it is set as a properties command value of the actuator 6 in each operating time.