Abstract: An enciphered facsimile apparatus in which encoded image data is fetched one block at a time, and chained encipherment is executed in a reverse direction, respectively. Upon completion of encipherment, the enciphered image data is read in the reverse direction, and is demodulated to transmit to a network. Meanwhile, on the reception side, the enciphered image data received is fetched one block at a time, and deciphering is effected in the reverse direction. Upon completion of deciphering, decoding is effected in the reverse direction so as to confirm whether or not deciphering has been effected correctly. Thereby, the image data enciphered cannot be readily deciphered by a third party.