1. A traffic-volume prediction device that predicts a traffic volume between points using travelling locus data of a vehicle collected in advance, comprising: a network creation device that extracts principal intersections based on a proportion of a maximum ramification number to a number passing through a traveling locus between intersections on a travel route in the travelling locus data and creates a simple network connecting the principal intersections one another, a model creation device that calculates a utility of a route between the principal intersections based on a property value between the principal intersections and estimates a parameter of a route selection model for evaluating a selection probability at each principal intersection based on the utility, and a traffic-volume assignment device that calculates the selection probability of selecting the route between the principal intersections based on the estimated parameter of the route selection model and distributes the traffic volume to the route for predicting the traffic demand based on the selection probability.