1. A drowsiness determination apparatus comprising: a decreased wakefulness detection means for detecting a sign of decreased wakefulness of a driver of a vehicle due to drowsiness, the sign of wakefulness detected from facial information; a struggle detection means for detecting a sign of struggle by the driver against drowsiness, the sign of struggle detected from the facial information; and a drowsiness determination means for determining a drowsiness level based on the sign of decreased wakefulness and the sign of struggle, wherein the drowsiness determination means determines no drowsiness when the sign of decreased wakefulness is not detected, determines drowsiness when the sign of decreased wakefulness is detected, and determines a drowsiness level according to presence or absence of the sign of struggle in a state determined to be drowsy.