A supervisory control system includes a supervisory control target device and a supervisory control device. The supervisory control device is configured such that an attribute usage flag that indicates whether the supervisory control device supports any changes in the attributes due to adding of a function, and an attribute effectiveness flag which indicates whether the supervisory control target device supports the changes, are added, as information concerning the attributes that undergo the changes, to a definition of the instance which the supervisory control device retains. Further, the supervisory control device includes a control unit which, on a basis of data of the attribute usage flag and attribute effectiveness flag relating to the attributes undergoing the changes due to adding of a function, determines whether the supervisory control target device supports a new function or whether supervisory control based upon the new function is effective.