PURPOSE: To warrant transmission of network control data regardless of aborting data resident in a reception buffer memory for a predetermined time or over.

CONSTITUTION: A reception buffer management means 101 gives time management data representing data storage permissible time to reception data coming from an interface and sends the result to a reception buffer memory 102. When a data transmission means 103 extracts data sent by the FIFO system, destination data extracted from a destination information table 104 are given to the sent data and the result is sent to a destination. In this case, a time monitor means 105 outputs a time elapse signal when time management data are zero. Then in-data contents discrimination means 106 reads the contents of the received data to discriminate whether the data are network control data or other data. In the case of the former data, an exception processing command means 107 outputs a data return command to the means 103 to return the data to an entry of the memory 102. In the case of the latter data, the means 107 outputs a data delete command to the means 103 to reserve the area the memory 102 for next reception data.