A design automaton extractor extracts a design automaton from design description data, and a property automaton extractor extracts a property automaton from property description data corresponding to the design description data. A matched state detector counts all states of the design automaton, detects matched states matching the property automaton from all the states of the design automaton, and counts the matched states. A coverage calculator obtains a ratio of the number of matched states to the number of all the states of the design automaton, thereby calculating a coverage representing the degree of correspondence of the property description data to the design description data.