An MFP sets an access condition for an external device with respect to a cloud box. The access condition is transmitted from the MFP to a relay device, and is registered in a memory of the relay device. When the relay device receives an access request made by the external device with respect to the MFP serving as an internal device, the relay device determines whether to permit or deny access to the MFP by comparing the access request with the access condition. When the access is permitted, the access request is transferred from the relay device to the MFP, whereas when the access is denied, the relay device notifies the external device of it.