PURPOSE: To reduce loads on a processor and a communication controller and to improve key control security by enciphering and deciphering a communication message for only a necessary part of transfer data by a channel device interposed between the processor and communication controller.

CONSTITUTION: The channel device 1 consists of a transfer means 11 and a partial enciphering means 12 and the transfer means 11 transfers the communication message between the processor 2 and communication controller 3. At this time, the partial enciphering means 12 executes partial enciphering and deciphering of the communication message. The partial enciphering means 12 is equipped with an enciphering means 121 which enciphers part of the transfer data transferred by the transfer means 11, a deciphering means 122 which deciphers the transfer data partially, and a nonvolatile memory 124 stored with a key for enciphering. Further, the device is equipped with an operation means 125 which sets and reads the key out from outside the device and a key control means 123 which sets the key with a command and takes the key out for enciphering and deciphering. Consequently, the key is controlled in safety without decreasing the CPU processing ability of the processor 2 or communication controller 3.