An anti-theft system for a vehicle includes an on-vehicle machine (10) including reporting means (28) configured to report by radio an illegal activity affecting the vehicle to a designated opponent to be reported to in a case where the illegal activity is detected; and an external facility (30), the external facility (30) including obstruction radio wave detection means (36) configured to detect a radio wave obstructing the radio-report by the reporting means; and illegal activity prevention means (38, 40, 42) configured to prevent the illegal activity in a case where the radio wave is detected by the obstruction radio wave detection means (36). Jamming the radio signal from the vehicle is detected and triggers taking a photograph of the vehicle and its surroundings.