PURPOSE: To prevent the state of system stop, by reading a management data of a channel device side to a processing device with one reading instruction.

CONSTITUTION: When a processor 3 provides an instruction indicating a polling transmission and if no response is obtained from a channel device 9 even after the prescribed time to be elapsed, a control section 4 sets a reading instruction C of a register 5 to an interface register 10. When an interruption reception section 13 receives this instruction C, the operation of a line controlling section 14 is stopped, a processing section 15 is started, and line data D in a region 17 of a memory 16 is transferred to a region 7 of a memory 6 via an interface register 11. The control section 4 checks the line management data D in the region 7, and provides an instruction F instructing the transmission of a polling signal P to a terminal device 20 detected with a failure and a forced reset signal to its input/output device 20.