1. A method of verifying an equivalence between a behavioral description and a register transfer level description, comprising the steps of: extracting, from a behavioral synthesis device for deriving a register transfer level description through a plurality of steps from a behavioral description, an associated relation between intermediate level descriptions subsequent to the respective steps and intermediate level descriptions prior to the respective steps; and checking the equivalence between the intermediate level descriptions prior and subsequent to the steps to verify the equivalence between the behavioral description and the register transfer level.