Data to be encrypted (301) is partially extracted successively. A result of encrypting a previously extracted portion of the data is used to successively calculate that of encrypting the currently extracted portion of the data successively. Successively calculated results of the encryption are used to generate encrypted data (305). In generating the encrypted data, a finally calculated result of the encryption (PF(z+1)) is attached to the generated encrypted data. The finally calculated result is used as falsification detecting data (308) for detecting whether the data to be encrypted is falsified data.