The object is to provide a drowsiness detecting device for detecting strong drowsiness to become a dozing state. A drowsiness detecting device 1 comprises a sympathetic parameter acquiring unit 2, 11 for acquiring a parameter concerning a sympathetic nerve of a subject, a parasympathetic parameter acquiring unit 2, 11, 16 for acquiring a parameter concerning a parasympathetic nerve of the subject, a sympathetic increase determining unit 13, 14 for determining whether the sympathetic parameter is greater than a sympathetic threshold or not, and a drowsiness determining unit 19 for determining drowsiness of the subject according to an increase/decrease relationship between the sympathetic and parasympathetic parameters when the sympathetic increase determining unit 13, 14 determines that the sympathetic parameter is greater than the sympathetic threshold.
