Inverted microscope

There is disclosed an inverted microscope comprising an objective lens disposed under a sample, a tube lens which is disposed in a light path of an observation light emitted from the objective lens and which forms the observation light into an image, an incident light illumination optical device which is disposed between the objective lens and the tube lens, and which introduces incident light illumination into the light path of the observation light, and an input/output port which is disposed between the incident light illumination optical device and the tube lens, and which splits a light flux from the light path of the observation light or introduces the light flux into the light path of the observation light.