An extraction unit of fault assumption and a finish-point FF is provided, the fault assumption is selected from fault assumption information, and a logic trace is executed from the fault assumption toward an output side. A test result of a finish-point FF obtained as a result of the trace from the fault assumption is determined. The maximum value and the minimum value of the propagation route up to the finish-point FF are determined, and a delay margin is determined from the values. A delay range is determined by using the delay margin and the test result, and a fault candidate and a delay range of the delay fault are specified by the process of the determination of the fault candidate and the delay range.