A paper sheets feature detector 20, through which a banknote 21 is carried and passed is provided with a carrying-in sensor part 22, a transmissive and reflective line light sensor 23, a magnetic sensor 24, a thickness sensor 27, and a carrying-out sensor part 28. When a watermark part of the banknote 21 is measured by the line light sensor 23, a watermark pattern is detected by a light transmissive sensor, and that pattern is not detected by a light reflective sensor, the banknote 21 is determined to be a true banknote. Watermark braille is similarly processed. When the thread is detected by the light transmissive sensor and the thread is not detected by the light reflective sensor, the banknote 21 is determined to be a true banknote.