There is provided a device control apparatus which makes it possible to dispense with device monitoring (polling) by a client apparatus to thereby reduce traffic on a network. A device server 200 acquires, according to device information for identifying a device locally connected to the device server 200, at least one of a trigger detection algorithm and a definition file for monitoring a state change of the device identified based on the device information, and monitors the locally connected device based on at least one of the acquired trigger detection algorithm and definition file. Then, when a state change of the device is detected, the device server 200 sends a trigger notification indicative of the detection of the state change to a client PC 100 via a network 500, and starts a session with the client PC 100 in response to a connection request from the client PC 100 having received the trigger notification.