To solve the problem that it is impossible to prevent a recorded medium from being illegally obtained because the recorded digital signals are reproduced with high quality when the recorded medium is illegally obtained.

This recording and reproducing system is provided with a digital signal recording device which generates a coded data string by ciphering, using coded information, either of the data strings divided into an odd numbered sample data string of the odd numbered samples and an even numbered sample data string of the even numbered samples of a digital signal and which combines the-coded data string with the non-coded data string and records them on a recording area of a recording medium, a storage device which stores the coded information in a storage area, and a digital signal reproducing device which reads the composite data string and the coded information from the recording medium; divides the composite data string into the non-coded data and the coded data; decodes the cryptography of the coded data string by using the coded information; and outputs the digital signal combining the noncoded data string with the decoded data string.