In a driver monitoring system, a pattern projecting device consisting of two fiber gratings stacked orthogonally which receive light from a light source projects a pattern of bright spots on a face of a driver. A image pick-up device picks up the pattern of bright spots to provide an image of the face. A data processing device processes the image, samples the driver's face to acquire three-dimensional position data at sampling points and processing the data thus acquired to provide inclinations of the face of the driver in vertical, horizontal and oblique directions. A decision device decides whether or not the driver is in a dangerous state in accordance with the inclinations of the face obtained. A warning device warns the driver against his dangerous state. The pattern light projecting device and pick-up device are integrated to each other and installed on a steering column on a vehicle. Thus, the driver monitoring system can assure performance, reliability and safety without hindering the driver in view of its installation on the vehicle.