An abnormality monitoring system includes gas sensors provided in the cavity or the vicinity of a tire provided in a vehicle, a determination unit that determines the presence of an abnormality in the tire on the basis of the detection results of the gas sensors, and an output unit that outputs data based on the determination result of the determination unit. The gas sensors detect a volatile substance when abnormal heat build-up occurs in the tire. The volatile substance is a substance derived from an additive added when a tire is manufactured.