A rigid-scope optical system includes: an image-formation optical system that causes an image in each of wavelength bands to be formed in a predetermined imaging device, the wavelength bands including a fluorescence wavelength band and a visible light wavelength band; and a color-separation-prism optical system having a dichroic film that separates an optical path of light to be imaged into an optical path of the visible light wavelength band and an optical path of the fluorescence wavelength band, in which the image-formation optical system causes the respective images to be formed in a fluorescence imaging device and a visible light imaging device, the fluorescence imaging device and the visible light imaging device being disposed to cause an amount of misalignment to correspond to a difference between an optical path length of fluorescence and an optical path length of visible light.