An observation device includes: an illumination optical system configured to emit illumination light to above a sample from below; and an objective optical system configured to acquire an image of transmitted light below the sample in a path different from a path for the illumination optical system, the transmitted light resulting from the illumination light that has been emitted from the illumination optical system, that has been reflected above the sample, and that has passed through the sample. The objective optical system includes, in the vicinity of a pupil plane, a pupil modulation element that partially decreases transmittance and that modulates the phase of light, and the illumination optical system includes a light source, and an illumination-region restricting section configured to restrict light from the light source to a particular emission region.