A microscope unit comprises: a main lens barrel of an imaging optical system; and an illumination lens barrel of an illumination optical system connected to the main lens barrel, the illumination optical system having: a collector lens that collects light that has been irradiated from a light source; a fly-eye lens allowing to be transmitted therethrough light from the collector lens; a first relay lens having lenses that relay light from the fly-eye lens; a field stop that stops down a range of light from the first relay lens; a second relay lens that relays to a beam splitter light from the first relay lens; and the beam splitter guiding at least a part of light incident thereon to the objective lens and allowing to be transmitted therethrough to a side of an imaging sensor at least a part of light incident thereon from the objective lens.