To facilitate control and make it easy to carry on a data communication, and prevent the traffic of a packet type digital communication network from increasing.

Mobile terminals 5a and 5b operate end to end according to protocol for data communication. Packet generation parts 32 of data communication controllers 3a-3c discard ineffective frames (β in figure) among frames F from the mobile terminals 5a and 5b which are received from line switching type digital communication networks 2a-2c through base stations 4a-4c. Then only the effective frames (α in figure) are stored and packets P containing the effective frames are sent to the packet type digital communication network 1.