A common-key blockcipher processing structure that makes analysis of key more difficult and enhances security and implementation efficiency is realized. In a key scheduling part in an encryption processing apparatus that performs common-key blockcipher processing, a secret key is input to an encryption function including a round function employed in an encryption processing part to generate an intermediate key, and the result of performing bijective transformation based on the intermediate key, the secret key, and the like and the result of performing an exclusive-OR operation on the bijective-transformed data are applied to round keys. With this structure, generation of round keys based on the intermediate key generated using the encryption function whose security has been ensured is performed, thereby making it possible to make analysis of the keys more difficult. The structure of the key scheduling part can be simplified, thereby making it possible to improve the implementation efficiency.