A large-scale content delivery system may be achieved, which may send a large amount of contents without intensive management of the contents in the server. In a service providing system where a client, a service gateway, and a server are connected to each other through a network, the client sends a first message to the server by way of the service gateway. The service gateway inquires a processing method of the first message from the client of the server by using a second message that includes a part of the first message content. The server replies to the inquiry of the processing method from the service gateway with a program that describes the processing method, and the service gateway processes the first message from the client on the basis of the received processing method.