To provide a data communication system by which a receiver can effectively utilize an IP address reported from a transmitter.

When the transmitter informs the receiver about the IP address by facsimile via PSTNs 112, 114, 116, and designates memory reception to the receiver, the receiver stores the IP address to be made correspond to a communication number. When the transmitter designates polling transmission of memory reception information to the receiver with a facsimile communication protocol via the Internet 118, the receiver informs a terminal about the IP address. Then the polling-received terminal selects reply, and starts facsimile communication via the Internet 118 by using the received IP address.