A system includes an input unit (2) to which failure information corresponding to failure modes of constituents indicating software and hardware, a system configuration information and a standard value of system availability are inputted, a producing unit (32) producing a fault tree based on the system configuration information, a calculating unit (34) calculating unavailability corresponding to the failure modes based on a result of analyzing the failure information, and calculating system availability based on the calculated unavailability and the fault tree, a determining unit (35) determining whether the system availability meets the standard value, an extracting unit (36) extracting a basic event related to an increase in the system availability when the system availability is determined to be below the standard value, and resetting units (38, 39) resetting new unavailability and the like based on whether it is possible to reduce the unavailability of the extracted basic event.