An imaging unit 2 captures an image of a driver of a vehicle. A driving state measurement unit 70 analyzes the image captured by the imaging unit 2 and measures a plurality of driving states including the driver's face orientation angle. A traveling state determination unit 71 determines the traveling state of the vehicle. An alarm determination unit 72 determines whether to activate an alarm device 5 on the basis of the driving states and the traveling state. When the face orientation angle acquired from the driving state measurement unit 70 is out of a normal determination reference range, and it is determined that the driving states other than the face orientation angle are normal and the traveling state is also normal, the alarm determination unit 72 causes the driving state measurement unit 70 to re-execute the face orientation angle detection process.