An endoscope apparatus includes an illuminator including: an emphasis light source that emits emphasis narrow band light whose peak or central wavelength is included in an emphasis wavelength range that includes a maximum wavelength taking a maximum value of an optical absorption spectrum of a diagnosis target substance or a largest wavelength taking a largest value of the spectrum in any of three color ranges and a non-emphasis light source that emits non-emphasis narrow band light whose peak or central wavelength is included in a non-emphasis wavelength range that is a wavelength range not including the emphasis wavelength range of the color ranges. The illuminator further includes a light quantity ratio changing section that changes a light quantity ratio between the emphasis and non-emphasis narrow band light.
