A tire state monitoring system includes: tire state acquisition devices installed on tires of a host vehicle, each of the tire state acquisition devices being configured to acquire a tire state quantity; a monitoring device configured to receive an output signal from each of the tire state acquisition devices and perform predetermined processing; and an alerting device configured to issue an alert to a following vehicle. In addition, the monitoring device causes the alerting device to operate when a predetermined abnormality has arisen in the tire state quantity.