PURPOSE: To enable obtaining sampling data at the same time from respective terminal equipments by transmitting a code signal for each terminal equipment from a central relay apparatus, by computing the transmission delay time of each terminal through a return signal from each terminal and by outputting a signal expecting said transmission delay time from said central relay apparatus.

CONSTITUTION: A signal coded for each terminal 8-1 to 8-3 is sent from the synchronous arithmetic circuit 4-1 in a central relay apparatus 1 to terminals 8-1 to 8-3 via an optical fiber cable(OFC) 9. The folded circuits 4-2 to 4-4 of respective terminals 8-1 to 8-3 fold only sampling signals attached with their own codes by transmitting said signals to the apparatus 1 via the OFC 10. The transmission delay time to each terminal 8-1 to 8-3 is obtained by said apparatus 1 and said sampling signal is outputted to each terminal 8-1 to 8-3 at any point of time after generation of a reference pulse and before the transmission delay time.