In a mutual authentication method for use between a recording apparatus which records copied contents on a recording medium having an arithmetic processing function, and the recording medium, the method includes a step of storing in the recording medium at least first information which depends on the recording medium, and second information which is to be shared by the recording apparatus in executing mutual authentication with the recording apparatus and depends on the recording medium, and a step of generating by the recording apparatus authentication information used in mutual authentication with the recording medium on the basis of the first information obtained from the recording medium, and executing mutual authentication between the recording apparatus and the recording medium using the generated authentication information and the second information.