A roadside device set to be installed at an intersection where a traffic light is installed, the roadside device includes an imaging unit configured to image a vehicle that enters the intersection, an input unit set to receive a state of the traffic light, and a wireless communication unit. When the traffic light for the vehicle is a red signal or is scheduled to switch to the red signal within a predetermined time, and a speed of the vehicle is equal to or greater than a predetermined threshold or the speed of the vehicle is increased, the wireless communication unit transmits information indicating that a runaway vehicle enters the intersection.