AbstractThis paper considers the case where the specification and the program are modified. A method is proposed that specifies the range which is affected by the modification using the verification method and decomposition technique. By the proposed technique, the points where the modification is required or the point which may contain an error can be estimated when the program is modified. The inductive assertion is used as the verification technique.It is assumed that the specification before modification as well as the program are already verified for the correctness. The object of verification is simplified by the comparison and validation of the verification history and the object of correctness verification. The part which is left without being simplified is the range affected by the modification before the comparison and after the correctness verification, the rage which is affected by the modification as well as the range for which the validation is not satisfies can be specified.