An intermediate device which can be introduced and removed in seamless way is disclosed. The state information acquiring means acquires state information required to maintain the state of a session established between the first information processing device and the second information processing device for the information processing service, from the first information processing device or the second information processing device. The intermediate service managing means generates, based on the state information, transfer rules for applying the intermediate service to data of the information processing service, and transferring the data to which the intermediate service is applied. The transfer control means maintains the state of the existing session between itself and the second information processing device, establishes a new session between itself and the first information processing device, and transfers the data using the existing session and the new session, according to the transfer rules.