Network control system which uses two timers and updates routing information

To provide a network control system which prevents a system performance degradation caused by generating/updating routing information and enables a connection request to be established reliably. The significant change detection module 33 sets the flag 33a to on when a pre-determined change occurs. The first timer 21 determines the longest interval at which the routing information 24 is updated, while the second timer 22 determines the shortest interval at which the routing information 24 is updated. When the first timer 21 times out, the routing information update control module 23 unconditionally updates the routing information 24. When the second timer 22 times out, the routing information update control module 23 updates the routing information 24 only if the flag 33a is on.