A management center analyzes probe information uploaded from an in-vehicle terminal mounted in each of multiple probe cars to thereby generate road traffic information allowing specification of a unit road segment in a congested state. The generated road traffic information is transmitted via a broadcasting station and terrestrial digital broadcasting. Each in-vehicle terminal includes a navigation device. The navigation device determines traffic congestion state relative to multiple unit road segments successively in accordance to traveling of the relevant probe car. Only when confirming a predetermined difference relative to each unit road segment between the determined traffic congestion state and the traffic congestion state indicated in the road traffic information received from the management center, the navigation device uploads to the management center the probe information collected with respect to the corresponding unit road segment by using a mobile communications terminal.