A driver monitoring device is provided. The driver monitoring device is provided with: a detecting unit (21) which detects a deterioration in the attitude of a driver on the basis of images of the driver's seat of a vehicle, captured by a camera (31); an assessing unit (22) which assesses whether or not the deterioration in the attitude of the driver detected by the detecting unit is a deterioration in attitude resulting from a habit of the driver; and notifying units (33 and 34) which notify the driver about the deterioration in attitude, in different modes depending on if the assessing unit has assessed that the deterioration in attitude is the result of a habit, or if the assessing unit has assessed that the deterioration in attitude is not the result of a habit.