An alarm device for a vehicle has a sensor section detecting that the hand of a passenger approaches an opening and closing operation section H and sending an operation detecting signal, a vehicle detector detecting another vehicle approaching from behind and sending a vehicle detecting signal, a vibration unit vibrating the opening and closing operation section H, a lamp section arranged on a pillar and displaying a warning sign with the irradiation of light, and a ECU (Electric Control Unit). When the ECU receives the vehicle detecting signal and the operation detecting signal, the vibration unit operates and a warning sign is displayed on the lamp section. Thereby, when another vehicle approaches, it is possible to prevent the passenger from opening operation of the door body.