DUPLEX CONTROL SYSTEM AND CONTROL METHOD THEREOF

PROBLEM TO BE SOLVED: To allow respective control devices to detect transmission abnormality in tracking bus in a duplex control system.SOLUTION: A duplex control system 1 comprises: two control devices 2, one of which is operated as a standby system and the other is operated as an operation system; tracking bus 3 that connects the two control devices 2 and causes tracking signals 21 to be transmitted and received; and a control transmission path 4 for transmitting arithmetic information of the two control devices 2. Each of the two control devices 2 individually includes: an own system state determination section 11 for transmitting a state determination result of own system to the other system as the tracking signal 21 via the tracking bus 3; an other system signal confirmation section 13 that receives the tracking signal 21 from the control device 2 of the other system via the tracking bus 3 and performs state confirmation; and a transmission path switching section for, in a case where the tracking signal 21 fails to be received via the tracking bus 3, causing the tracking signal 21 to be transmitted to the other system signal confirmation section 13 of the other system via the control transmission path 4.