PURPOSE: To aviod the opportunity of system down, by providing the set which detects the jam of data delivery control in case of failure and resets the entire station, with the data delivery control circuit of the station connected in loop.

CONSTITUTION: In the delivery control unit with the constitution that a plurality of stations 3 to 5 and the control station 2 are connected to the delivery line 1 connected in loop, the input 21 is connected to the line control circuit 13 via the reception circuit 21 and the output of the circuit 13 is outputted to the output 22 via the transmission circuit 12. The circuit 13 is provided with the reception control circuit 14, GA detection circuit 15, transmission control circuit 16, and selector switch 17, and in the normal condition, the operation of the reception and transmission is made with the instruction of the microprocessor 19. Further, if jam is taken place to the control step in the station, it is detected with the timer circuit 18 connected to the circuit 15, and the output of the circuit 18 selects the switch 17, the reset circuit 20 returns the entire set to the initial state, preventing the system down.