PURPOSE: To allow one processor to implement the conversion of plural kinds of communication protocols by using a program transferred in a file form from a file memory, thereby converting the communication protocol.

CONSTITUTION: An active processor 10 can correspond with the conversion of plural kinds of communication protocols by using a different program, A standby processor 11 implements the processing of communication protocol conversion on behalf of the processor 10 when it is faulty. A file memory 4 stores programs for communication protocol conversion. A signal reception unit 3 decides the communication protocol conversion required at the reception of a setting request and transfers the program required for the execution to the active processor 10. A fault monitoring unit 8 monitors the fault of the active processor 10 and transfers the same program used for the active processor 10 to the standby processor 11. Thus, plural kinds of communication protocols are converted by one processor.