An illuminator (20) of an endoscope apparatus (10) includes: laser light sources (44-1 44-3 44-5) that emit first emphasis narrow band light whose peak wavelength or central wavelength is included in an emphasis wavelength range, the emphasis wavelength range including, for an optical absorption spectrum of a diagnosis target substance present in an observation object (0), at least one of a maximum wavelength that takes at least one maximum value and a color-range largest wavelength that takes a color-range largest value that is a largest value of the optical absorption spectrum, in any of three color ranges that are a blue range, a green range, and a red range lase light sources (44-244-444-6) that emit first non-emphasis narrow band light whose peak wavelength or central wavelength is included in a non-emphasis wavelength range, the non-emphasis wavelength range being a wavelength range that does not include the emphasis wavelength range of the three color ranges and a light quantity ratio changing section (72) that changes a first light quantity ratio that is a light quantity ratio between the first emphasis narrow band light and first non-emphasis narrow band light included in the rays of narrow band light.
