A sample observation device includes an illumination optical system and an observation optical system, and the illumination optical system includes a light source, a condenser lens, and an aperture member, and the observation optical system includes an objective lens and an imaging lens, and the aperture member has a light-shielding part or a darkening part, and a transmission part, and the transmission part is located outside of an outer edge of the light-shielding part or the darkening part, and an image of an inner edge of the transmission part is formed inside of an outer edge of a pupil of the objective lens, and an image of an outer edge of the transmission part is formed outside of the outer edge of the pupil of the objective lens, and the following conditional expression is satisfied. 0.005≤Ratio≤0.9.