Data to be transferred from a BUS1 (IEEE 1394 or USB) is encrypted by a second encryption process (DES) and the encrypted data is written to an external SDRAM through an external terminal of a data transfer control device. The encrypted data that has been written to the SDRAM is read through the external terminal, and the thus-read encrypted data is transferred to a BUS2 to which an HDD is connected. Encrypted data transferred from the BUS1 is decrypted by a first decryption process (DTCP), and is written to a small-capacity SRAM within the data transfer control device. The thus-written decrypted data is read from the SRAM and encrypted by the second encryption process. Paths that bypass the second encryption (or decryption) are also provided.