PURPOSE: To prevent the effect of congestion onto all subscribers and the interruption of a restricted subscriber.

CONSTITUTION: A line control section 1 makes queuing of a reception packet memory to a packet reception storage area 4 to allow a reception packet to take over a packet processing section 2. A processing wait packet counter section 6 adds 1, a threshold level over is discriminated and a restriction signal is sent to set the restriction mode. A packet processing section 2 decrements a processing wait packet counter 6 by 1 after the end of packet processing, detaches a reception packet from a packet storage area, discriminates '0' when the line is under restriction, requests restriction release to the line restriction section 1 and sends a restriction release signal to inform restriction release to the subscriber. A line monitor section 3 monitors the processing wait packet counter section 6 and the line restriction state for each unit time and initializes the processing wait packet counter section 6 when the processing wait packet number does not exceeds the threshold level not in the restriction state.