Upon startup of an OS, the present invention obtains an entry of a StatusMonitor key from all printer driver setting information subscribed in a registry by means of a subscriber (S0), and if a value thereof is 1, obtains an entry of a key including “Notification”. If a value of an array element 0 indicates activation of notification, the present invention obtains a character string of an array element 1 as an event type, and makes a Subscribe request to an image forming apparatus (S3). The present invention stores a subscription ID being returned, and makes an Unsubscribe request to the image forming apparatus for all subscription IDs thus stored, upon shut-down of the OS.