Endoscope system and fluorescence imaging method

An endoscope system, comprising:

• a non-visible light source configured to emit first excitation light and second excitation light onto a target in which a fluorescent chemical having a wavelength band being capable of emitting fluorescence has been given, the first excitation light having a half width of not more than 10 nm and a first wavelength of a non-visible light band, the second excitation light having a half width of not more than 10 nm and a second wavelength of the non-visible light band being different from the first wavelength, a difference between the first wavelength and the second wavelength being at least 20 nm, each of the first wavelength and the second wavelength being within a first range of 750 nm to 810 nm;
• an image sensor configured to generate an image including the target excited by at least one of the first excitation light and the second excitation light such that fluorescence of the fluorescent chemical is emitted;
• an optical filter that is disposed on an incidence side of the image sensor and that is configured to shield the first excitation light and the second excitation light, wherein the optical filter has a characteristic that transmittance of the optical filter is not higher than 0.1% with respect to the wavelengths of light throughout a second range of 690 nm to 810 nm, the optical filter providing for transmittance of light at least throughout a third range from 380 nm to 690 nm and a fourth range including 830 nm;
• and
• an output configured to output the image.