By overlapping lighting timings of light sources that emit lights of a plurality of different wavelength bands including a wavelength band of at least a visible light region and an infrared light region, the lights of the plurality of the different wavelength bands including the wavelength band of at least the visible light region and the infrared light region are emitted on a banknote while securing an overlap in timings thereof. Moreover, by using light receiving elements each including a bandpass filter that allows only light of a wavelength range that corresponds to the wavelength band of each of the light sources, received light intensities of the light of the wavelength range that corresponds to the wavelength band of each of the light sources are acquired simultaneously, and image data are formed based on the received light intensity of every acquired wavelength band.