PURPOSE: To prevent missing of data during data transfer by providing a file device storing a data in a transmission buffer an a response supervisory means detecting unarrival of a response signal from a processing unit, to a terminal device.

CONSTITUTION: A terminal device 1 stores a data D from an input section 6 to registers B1∼B8 of a transmission buffer 5 to transmit the said data to a center 3 via a switch 7 and a transmission/reception section 8. The center 3 receives the data at its transmissin/reception section 9 and stores it in a reception buffer 4. The processing unit 10 stores the data to a file device 11 and also transmits a response signal A to the terminal device 1. If no signal A is returned because of power failure or the like at the center 3, the control section 12 of the terminal device 1 confirms the unarrival of the signal a after a prescribed time is elapsed in a timer 13 and the switch 7 is switched by a signal C and data D1∼D8 of the buffer 5 and an input data I are stored in a file device 15 via a file control section 14. When the power failure of the center 3 is restroed, then the unit 10 generates a transfer request R, the terminal device 1 transmits the data in the file 15 and restores the switch 7.