A traffic volume determination system includes a processor configured to: calculate, while taking account of a change between a past traffic volume and a current traffic volume of vehicles passing through an area around a link, an estimated value of the current traffic volume of the vehicles passing through the link from the past traffic volume of the vehicles passing through the link; and determine that the link is closed when a current actual traffic volume of the vehicles passing through the link is smaller than the estimated value of the current traffic volume of the vehicles passing through the link by more than a statistical error.