The present invention provides an information recording medium and an information treatment method. It is possible to prevent unauthorized copying of recorded information and flexibly operate a content. Furthermore, it is possible to facilitate improvement of the copy prevention technique. A key acquisition module (2) is recorded on an information recording medium (1) dedicated to reading and having the copy prevention technique. A reproduction module (3) safely acquires a medium key inherent to the key acquisition module (2) from the key acquisition module (2), generates a content key from the medium key, decrypts the encrypted content (4) by using the content key, and reproduces it. Here, the key acquisition module (2) should be resident on the information recording medium (1) while thereproduction module (3) and the encrypted content (4) need not be on the information recording medium (1) but may be outside the information recording medium (1).