1. A safety verification device of a reactive system represented by a set of function symbols, a set of rewriting rules, a set of axioms, a set of terms, and a set of terms to be verified, said set of axioms being a set consisting only a commutative law and an associative law, and said safety verification device of a reactive system comprising: a translation unit generating, under said set of axioms, a first equational tree automaton which accepts said set of terms; a simulation unit generating, under said set of rewriting rules and said set of axioms and using said first equational tree automaton as initial data, a second equational tree automaton which accepts said set of terms and a set comprising terms derived from said set of terms; and a set operation unit which generates a fourth equational tree automaton by associating said second equational tree automaton with a third equational tree automaton which accepts said set of terms to be verified and determines whether or not a set accepted by the fourth equational tree automaton is an empty set.