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.