To provide a backup system capable of improving mounting efficiency while reducing the cost.

A shared data accumulation device 10 accumulates activation parameter information and the latest state of each of N individual processors (1)1, (2)2 to (N)3 of a current system, and transfers, when any one of the individual processors of the current system, for example, the individual processor (1)1 functions abnormally, the activation parameter information and latest state of the individual processor (1)1 laid in the abnormal state to a spare device 11 to activate it. Each of the N individual processors of the current system transfers the latest state to the shared data accumulation device 10 every time when the latest state is updated by execution of individual processing. The shared data accumulation device 10 detects abnormality in each of the N individual processors of the current system by transmitting polling data for requesting return of an answer showing existence/non-existence to each of the N individual processors of the current system at predetermined intervals or periodically and confirming the answer from each processor.