An event is classified as a fault of hardware or a fault of a system or a control system. When the event is classified as the fault of the hardware, the event is expanded into lower events, physical quantities of the event and the lower events are acquired, and it is examined whether the event is expanded properly or not based on relationship between the physical quantity of the event and the physical quantities of the lower events. When the event is classified as the fault of the system or the control system, a block diagram of the system or the control system is created, and the event is expanded into the lower events based on input/output relationship in the block diagram of the system or the control system.