A random number sequence is previously generated by the function f8 for data confidentiality processing, which generates a random number sequence, and stored in a random number sequence memory (buffer). When data (message) is input, the random number sequence stored in the random number sequence memory is obtained, and the data (message) is encrypted by an XOR circuit to generate ciphertext data. In case of decrypting data, a random number sequence is also previously generated by the function f8 for data confidentiality processing and stored in the random number sequence memory (buffer). When the ciphertext data is input, by the XOR circuit, the random number sequence stored in the random number sequence memory is read and the ciphertext data is decrypted into the data (message).