This invention provides a method of connecting a network-connected image input device, to which a plug-and-play function cannot be applied to a computer installed with an OS (operating system) and using the image input device. To this end, when a control program of the image input device is activated, the program notifies the OS of information indicating that the peripheral device is connected, irrespective of connection/non-connection between the peripheral device and the computer. Upon reception of a command for activating the peripheral device, the control program confirms the connection/non-connection between the peripheral device and the computer. When the connection is confirmed, the control program controls the peripheral device to activate.