PURPOSE: To accomplish the restarting of a system within the shortest period by checking the status of each doubling device at the switching of the system in case of a system trouble by a means for storing the status of each doubling device and also using a storage device of which contents can be insured.

CONSTITUTION: A control unit CC#1 is started by switching operation and then a discrimination circuit ANN1 is also started. A comparator CMP checks whether a main storage device MM#1 is normal or not. If no trouble is detected, a signal N is outputted and a phase 1 is restarted from the MM#1. If the contents of a main storage device MM#0 is incorrect, an output Y starts a discrimination circuit ANN4, which checks a status signal FM0. When a FM#1 is normal, restarting (RSFM) is started. When the FM#1 is incorrect, a discrimination circuit ANN5 checks the status of a magnetic storage device CMT. When the CMT is normal, restarting RSCMT is started. When the CMT is defective, the MM#1 executes the restarting (RSMM). When the MM#1 is defective, the FM#1 is checked and, when the FM#1 is normal, it starts restarting. If FM#1 is defective, the CMT is checked; the restarting is started in case of the normal CMT and the system is downed by the defective CMT.