A roadside information processing system according to the present disclosure includes a plurality of roadside devices installed on a roadside of a road and capable of communicating with a vehicle travelling on the road, and a plurality of sensors installed on the roadside to perform sensing on the road and its periphery, wherein at least one of the roadside devices includes an edge-server processing unit to obtain first information from in-vehicle devices included in the vehicles and from some of the plurality of the sensors, the first information indicating information about a periphery of the vehicles and about the road and its periphery, and to generate second information by using the first information, the second information indicating a position of the vehicles, a movement direction of the vehicles, and traffic jam conditions on the road.