1. A recording and reproducing apparatus for use with a disk-shaped recording medium which includes a transparent substrate and an optical recording layer formed on the transparent substrate, the apparatus comprising: a light source for emitting light; an optical head for applying the light to the optical recording layer from the light source via the transparent substrate, for focusing the light on the optical recording layer, and for reproducing information from the optical recording layer; a position detecting means for detecting at least one of a pit depth and a physical position of information which has a first given relation with a specified address and which is recorded on the recording medium, and for generating first positional information representing at least said one of the pit depth and the physical position; a reproducing means for reproducing a previously-recorded secret code from the recording medium, the secret code representing second positional information, and for decoding the secret code into the second positional information, the second positional information representing at least one of a predetermined reference pit depth and a predetermined reference physical position; a collating means for collating the first positional information and the second positional information, and for checking whether or not the first positional information and the second positional information are in a second given relation; and a stopping means for, in cases where the first positional information and the second positional information are not in the second given relation, stopping at least one of outputting of a reproduced signal of the recording medium, operation of a program stored in the recording medium, and decoding of the secret code.