an epi-illumination phase contrast microscope including an illumination light beam source, an illumination optical system emitting an illumination light beam from the illumination light beam source to an observation target which is a biological cell, and an observation optical system forming an optical image of the observation target from one or more reflected light beams obtained by reflection of the illumination light beam after passing through the observation target;

a moving device moving the epi-illumination phase contrast microscope relative to the observation target, the illumination optical system and the observation optical system being configured to be moved integrally by the moving device;

the observation optical system including a phase plate changing a phase of a directly reflected light beam reflected on a reflection surface among the reflected light beams;

both the illumination optical system and the observation optical system being arranged under the observation target;

an image pickup device photoelectrically converting the optical image obtained by the observation optical system to create image data of the observation target;

a display device displaying the image data,

wherein the illumination light beam emitted from the illumination optical system and passing through the observation target is a collimated light beam which is parallel to optical axes of the illumination optical system and the observation optical system; and

an incubator including a chassis having an opening, a lid body capable of opening/closing the opening, and a partition wall partitioning an internal space defined by the chassis and the lid body into a culture chamber in an upper portion of the internal space and a machine chamber in a lower portion of the internal space, wherein

the observation target is arranged in the culture chamber,

the illumination light beam source, the illumination optical system and the observation optical system, including a first objective lens, a second objective lens, the phase plate, and a half mirror, along with the image pickup device, and the moving device are arranged in the machine chamber,

the partition wall is fixed to the chassis such that the culture chamber maintains airtightness and watertightness against the machine chamber, and

at least one part of the partition wall is formed of a transparent material transmitting the illumination light beam.