A traffic volume determination system includes a table configured to store information indicating a statistical proportion of vehicles flowing into an exit link exiting from a node, among vehicles traveling on an entry link entering the node; an estimation unit configured to calculate an estimated value of a traffic volume of vehicles traveling on the exit link from an actual traffic volume of the vehicles traveling on the entry link, with reference to the table; and a determination unit configured to determine that the exit link is closed when the actual traffic volume of the vehicles traveling on the exit link is smaller than the estimated value.