1. A communication system comprising: an information providing unit configured to provide information data; an information providing-side network configured to connect the information providing unit and be restricted access; an information transmitter configured to obtain the information data by transmitting request data for requesting the information data to the information providing unit, and transmit obtained information data to a terminal; an information transmitting-side network configured to connect the information transmitter and be restricted access; and a transfer unit configured to connect the information transmitting-side network and the information providing-side network, determine whether or not transmitting-side data received via the information transmitting-side network is data transmitted from the information transmitter, and whether or not providing-side data received via the information providing-side network is data transmitted from the information providing unit, and transfer the transmitting-side data and the providing-side data based on determination results.