PURPOSE: To obtain a data exchange in which a missing of inter-station message missing due to the congestion of processings by a transmit/receive processor or the congestion of processings in an exchange processing processor does not occors.

CONSTITUTION: The transmit/receive processor 11 is provided with a buffer capacity monitoring section 15 monitoring a message storage quantity to an exchange processing processor 12 and informing the exchange processing processor 12 of it when it is detected that the quantity exceeds processing value, and the exchange processing processor 12 is provided with a buffer capacity monitoring section 21 monitoring a message storage quantity to the transmit/ receive processor 11 and informing the transmit/receive processor 11 of it when it is detected that the quantity exceeds processing value.