A distributed control device in a decentralized supervisory control system comprises an I/O interface, a data storage section for storing PIO data from a controller and additional information such as data obtention time, a time obtention section for adding a time to the data when the data is stored in the data storage section, a data distribution section for distributing the PIO data and other supervisory information, a supervisory control section for carrying out supervisory control using the PIO data from the controller, a network interface for communicating with other distributed control devices and the supervisory device, and a communication section for connecting this distributed control device to the other distributed control devices and the supervisory device.