An encryption/decryption device includes an encryption/decryption processing section which performs encryption or decryption processing for divided data of first and second content data in an operation mode of a block cipher method using data in a block other than a block under processing, and an intermediate value storage section which stores a processing result or an input value of the encryption/decryption processing section in content units. After the processing result or the input value of the encryption/decryption processing section for one of the divided data of the second content data has been stored in the intermediate value storage section, the processing result or the input value for the Kth divided data of the first content data is read from the intermediate value storage section, and the encryption/decryption processing section performs the encryption or decryption processing for the (K+1)th divided data of the first content data by using the processing result or the input value.