A recording and reproducing apparatus is provided in which recording and reproducing are performed with respect to an existing format cassette having an existing erroneous erasure prevention switch for preventing erroneous erasure of data recorded with the existing format and a new format cassette having a first erroneous erasure prevention switch located at a position corresponding to the position of the existing erroneous erasure prevention switch and having a second erroneous erasure prevention switch for preventing erroneous erasure of data recorded with a new format; wherein at the time of reproduction whether it is the existing format cassette or the new format cassette is judged based on data obtained from the reproduction of the existing format and new format cassettes to reproduce the cassette. Hereupon, in the new format cassette, the first erroneous erasure prevention means is always kept in a state of preventing the erroneous erasure.