To provide an antitheft device for a vehicle capable of improving antitheft effect for a vehicle by positively threatening a person trying to steal the vehicle.

On a scooter 11, a key hole lock device 13 is installed at a prescribed position around a steering unit 12 to be integrated with an ignition key switch 14. In the ignition key switch 14, a key hole 16 in which an ignition key 15 can be inserted is formed. On the key hole lock device 13, a shutter 17 which can be rotated by a shutter drive, an LED 18, a light radiation part 38a of a light reflection type sensor, and an alarm are installed. As the ignition key 15 is removed from the key hole 16, the shutter 17 is rotated to cover the key hole 16. The LED 18 flashes, and alarm sound is outputted from and the alarm at a prescribed interval. As a body of a person or the like gets closer to the light radiation part 38a, the alarm sound becomes louder.