An encryption key generation circuit for generating at least one 128-bit round sub key used in at least one sub round for encryption of 128-bit plaintext, from an encryption key having 64n bits (2n4; where n is an integer) includes a byte rotation circuit for performing byte rotation of rotating (8n+1)-byte information by 1 byte; a 3-bit rotation circuit for performing 3-bit rotation of rotating bits in each byte of the (8n+1) -byte information by 3 bits; and 16 adders for adding a 128-bit bias value to (8n)-byte information from the byte lowest of the (8n+1)-byte information processed with the byte rotation and the 3-bit rotation, so as to generate one of the at least one 128-bit round sub key in each sub round.