A state determination device includes a calculator that receives multiple eye region images captured at different timings in a time interval from when a person opening eyes closes the eyes to when the person opens the eyes next and calculates a luminance value relating to multiple pixels included in each of the eye region images and a determiner, wherein the determiner calculates a time interval from a first time point when the luminance value relating to the pixels reaches a predetermined first luminance value for the first time to a second time point when the luminance value relating to the pixels reaches a second luminance value after the first time point; if a time interval from the first time point to the second time point is a first time interval, the determiner determines that the person is in a first state; if the time interval from the first time point to the second time point is a second time interval which is shorter than the first time interval, the determiner determines that the person is in a second state which differs from the first state; and the determiner outputs a determination result.