In a disk array system, multiplexed clusters and multiplexed power source units for supplying power sources to the respective clusters are arranged. Each cluster has a power failure judging unit for judging the power source condition of other cluster. In response to a case where one cluster stops its operation first owing to a power failure, at the power failure, for example, MP of the cluster blocks the portion of the other cluster, and judges the power source condition of the other cluster on the basis of a signal from the power failure judging unit, and records power failure information showing the power source condition to a memory. At power recovery, if the cluster recognizes that the portion in blocked condition of the other cluster is in blockage owing to the power failure, the cluster recovers the portion.