In an embodiment of this invention, a diagnosis engine refers to a risk assessment DB and anti-risk measure DB, calculates along the time sequence a risk estimate amount in case of failure for each device and a maintenance cost in executing a measure method in advance, and adds the risk estimate amount and maintenance cost along the time sequence to calculate an optimum maintenance period of the device. When a failure has occurred in the device, the diagnosis engine refers to a failure diagnosis DB on the basis of the identification information of the device and the failure mode and analyzes, on the basis of an operation record, a failure which is different from a secular change.