A relay device for properly causing an information processing apparatus to process a Web service request from an external apparatus even when a firewall exists between the information processing apparatus and the external apparatus or even when the information processing apparatus exists in an environment in which address translation is performed. A mediation application of a mediation apparatus transmits a request corresponding to an operation on an operation screen displayed on an MFP, to a server, and receives a response to the request from the server. The mediation application determines to which of a Web browser and a service provider section of the MFP according to the content of the response. The mediation application transmits the response to one of the Web browser and the service provider section according to a result of the determination.