1. A property description coverage measuring apparatus comprising: a processor comprising: a design automaton extractor configured to extract, from design description data, a design automaton representing a state transition of the design description data; a property automaton extractor configured to extract, from property description data corresponding to the design description data, a property automaton representing a state transition of the property description data; a matched state detector configured to count all states of the design automaton, detect matched states matching the property automaton from all the states of the design automaton on the basis of the presence/absence of an automaton simulation relation from the design automaton to the property automaton, and count the matched states, the matched state detector classifies the matched states in the design automaton into equivalence classes on the basis of an equivalent relation between two arbitrary states on the design automaton, which simulate the same state on the property automaton, and counts the equivalence classes; and a coverage calculator configured to obtain a ratio of the number of matched states to the number of all the states of the design automaton, thereby calculating a first coverage representing a degree of correspondence of the property description data to the design description data.