A drowsiness detector capable of detecting light drowsiness of a subject with high precision is provided. The drowsiness detector acquires the measurement data of a measurement device first, and acquires a value of the pulse rate by performing preprocessing on the measurement data and extracts a pulse fluctuation from the value of the pulse rate. Then, the drowsiness detector sets the reference section width of the pulse feature value referred to in order to acquire the standard deviation of the pulse feature value (value of the pulse rate and pulse fluctuation) and then calculates the standard deviation value of the pulse feature value in the reference section width and acquires the corrected standard deviation value of the pulse feature value by dividing the standard deviation value of the pulse feature value by the pulse feature value. Then, the drowsiness detector determines whether or not the driver is lightly drowsy using the corrected standard deviation value of the pulse feature value.
