Information or contents cannot be reproduced even from a regular storage medium which is encrypted in accordance with a predetermined encryption system, due to erroneous detection of watermarks. Detection of the watermarks and restriction over reproduction depending thereon is conducted only in a case where the medium is not encrypted. In case of detecting that the data is not encrypted in accordance with a predetermined encryption system by an encryption detection circuit and when the watermarks are detected by a watermark detection circuit, reproduction of the data is stopped by a reproduction restricting circuit. In a case that it is detected to be encrypted in the predetermined encryption system by the encryption detection circuit, the reproduction restricting circuit will not stop the reproduction thereof.