An inspection device supports work related to ensuring security by including: a conversion unit that converts a regular expression of a first signature into a first representation by a nondeterministic finite automaton and converts a regular expression of a second signature into a second representation by a nondeterministic finite automaton; a determination unit that determines the presence or absence of an inclusive relationship between the first representation and the second representation; and an output unit that when a result of determination by the determination unit indicates that the first representation and the second representation have an inclusive relationship, outputs information indicating that the first signature and the second signature have the inclusive relationship.