PURPOSE: To always secure a logical information line with a network controller by permitting a packet exchange equipment to reject the blocking instruction of a trunk circuit when the packet exchange equipment judges that the logical information line to be used by itself is eliminated.

CONSTITUTION: When the network controller N4 transmits a circuit blocking signal which blocks a trunk circuit L31 to the packet exchange equipment P3, the P3 transmits a setting request signal to U10 through a logical information line setting part U30 and L31 in such a way that the logical information line is caused to be newly set between U10 and N4. When L31 is blocked here, it is judged that the logical information line cannot be set between P1 and N4, and P1 cannot receive setting recognition information from N4. A logical information line setting impossible signal is returned to P3 through L31 and U30. The P3 which has received the signal rejects the blocking instruction of L31 from N4 while P1 becomes independent of the packet exchange network.