Main data and a sub code supplied from input terminals 1a and 1b are processed by encoders 2a and 2b, respectively. The encoded main data and sub code are supplied to an EFM modulating portion 4 through a multiplexer 3. The EFM modulating portion 4 is composed of an 8-14 converting portion 5a and a connection bit selecting portion 5b. For the EFM modulating portion 4, a DSV normal controlling portion 7a and a DSV special controlling portion 7b are disposed. In only a predetermined region designated on an optical disc, the DSV special control is performed. The DSV special control causes the absolute value of the DSV to increase so that data will be prevented from being normally reproduced. The normal control causes the absolute value of the DSV to converge at 0. When data is reproduced from the optical disc, if the reproduction state of the predetermined region is abnormal, it is determined that the disc is an original disc. An encryption key can be recorded in the predetermined region.