PURPOSE: To manage a communication sequence and to decrease redundancy by collating a code type between a receptible code display flag string with that of a received data and deciding whether or not the received data is adequate on the communication sequence.

CONSTITUTION: A transmission/reception control module 3 gives a reception data 6 to a reception enable deciding module 2. On the other hand, a host module 4 writes status information on the communication such as a code type of a transmission data sent finally and a code type 7 of a received data 6 received finally to a communication control information table 5 in real time. Then the reception propriety deciding module 2 references the flag of a relative location corresponding to the code type 7 of the received data 6 given from the transmission/reception control module 3 among receptible code display flag strings 1 selected based on the status information of the communication control information table 5, decides it to be receptible when the flag is set and to be reception disable if the flag is reset and informs the result of decision to the host module 4.