A monitoring apparatus receives, according to an occurrence of an event (e.g., error or jam) at an image forming apparatus, a notification of information regarding the event that has occurred. The notification is sent with use of address information of the monitoring apparatus registered in the image forming apparatus. The monitoring apparatus stores the received information in a memory unit thereof. Then, the monitoring apparatus acquires the information regarding the event that has occurred at the image forming apparatus by periodically inquiring to the image forming apparatus, and determines whether the acquired information is stored in the memory unit. According to determination that the acquired information is not stored in the memory unit, the monitoring apparatus re-registers the address information of the monitoring apparatus into the image forming apparatus.