An opening is formed in resin 20 by a laser beam so that a via hole is formed. The low-resolution light source and first optical system are positioned so as not to physically interfere with the high-resolution light sources and first optical system, and so as to allow the set of beams from the low-resolution light source to scan an image forming area on the predetermined photoreceptor along a main-scanning direction. The first-level aggregated test results include a sum of the data points, a count of the number of the data points, a sum of squares of the data points, and an average of the data points. 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.