A common-key blockcipher processing configuration with enhanced immunity against attacks such as saturation attacks and algebraic attacks (XSL attacks) is realized. In an encryption processing apparatus that performs common-key blockcipher processing, S-boxes serving as non-linear transformation processing parts set in round-function executing parts are configured using at least two different types of S-boxes. With this configuration, the immunity against saturation attacks can be enhanced. Also, types of S-boxes present a mixture of different types. With this configuration, the immunity against algebraic attacks (XSL attacks) can be enhanced, thereby realizing a highly secure encryption processing apparatus.