A remote maintenance system capable of reducing user's time and effort required to establish communication between an image processing apparatus and an operator terminal. An operator terminal performs remote maintenance communication with an image processing apparatus via a relay server, for performing a maintenance operation of the image processing apparatus. A connection request for connecting to an operator terminal is received from an image processing apparatus, and the remote maintenance communication between the image processing apparatus and the operator terminal is established based on the connection request. When the connection request is received, an operator terminal that has not established the remote maintenance communication is assigned to an image processing apparatus that has sent the connection request, and the remote maintenance communication between the image processing apparatus having sent the connection request and the assigned operator terminal is established.