A scrambling key information piece is periodically changed among a plurality
of
different key information pieces including first and second key information pieces.
An input signal is scrambled into a scrambling-resultant signal in response to
the periodically changed scrambling key information piece. The scrambling-resultant
signal, the first key information piece, and the second key information piece are
recorded on the recording medium. The first key information piece which is used
in the scrambling of a portion of the input signal recorded during a first recording
interval is recorded on the recording medium during a second recording interval
being longer than the first recording interval and containing the first recording interval.
