The program control of network devices, each of which provides services according to the present invention, monitors a function of a program module operating in each of the network devices. If the function of the program module has a problem, the program control performs proxy response processing of the network device by a virtual device program until the problem is corrected. In addition, if thefunction of the program module has a problem, the program module operating in the network device is updated to the latest program module to correct the problem. Then, the operation of the virtual device program is stopped. Thus, among devices which operate in cooperation with one another by use of a communications protocol such as UPnP, even if there is a device having a device program that includes a bug, or even if there is a device that has a performance problem, the devices can operate in cooperation with one another.