A transport header analyzing unit (133) analyzes, on the basis of the TCP header of transport data transmitted from a transmitter terminal (100) to a receiver terminal (200), whether the transport data is an acknowledgement response in a TCP communication. If the transport data is not an acknowledgement response, a synchronization pre-processing unit (134) determines, on the basis of the TCP header of the transport data, whether synchronization information, which is required to operate in a power saving mode together with an access point (300), is added to the IP header of the transport data. A synchronization information processing unit (235) adds, to the IP header of the transport data indicating an acknowledgement response to received data that is received from the transmitter terminal (100), the synchronization information that is required to operate in the power saving mode together with the access point (300).