PROBLEM TO BE SOLVED: To properly determine states of drivers on the basis of a change in pupil diameter using an illumination unit provided in a vehicle.SOLUTION: A driver state determination device (a control unit 10) has: a pupil diameter detection unit 11 that detects a pupil diameter of a driver an illumination unit operation state detection unit 12 that is provided in a vehicle, and detects an operation state of an illumination unit irradiating the driver with light and a driver state detection unit 13 that determines a state of the driver on the basis of the pupil diameter detected by the pupil diameter detection unit 11. When the illumination unit operation state detection unit 12 detects that the illumination unit is lighted or brightness of the lighting illumination unit is greater, the pupil diameter detection unit 11 is configured to start detection of the pupil diameter of the driver, and continuously implement the detection during prescribed time, and the driver state determination unit 13 is configured to determine the state of the driver on the basis of a change in pupil diameter detected during the prescribed time by the pupil diameter detection unit 11.SELECTED DRAWING: Figure 4
