The present invention relates to an apparatus and a method for protecting the copyright of an information signal recorded on a recording medium such as a DVD (Digital Video Disc) for presenting the signal to the user or an information signal transmitted through transmission media such as the Internet and for preventing an illegal copy of such an information signal. To put it in detail, information on copyright protection which is read out from the recording medium and information on copyright protection which is encrypted to make the information difficult to alter is used. If both of the information do not match each other, the information on copyright protection is judged to have been altered in an attempt to play back the information signal which is obtained as a result of an illegal copy operation in which case, the operation to play back the information signal is disabled.