An inverted fluorescence microscope is described which irradiates an excitation light onto a sample for observation of a fluorescent image of the sample. The fluorescence microscope includes (a) a transmissive illumination light source, which is arranged above a stage for placing the sample and the transmissive illumination light source is arranged facing a horizontal direction; (b) a tilt mirror, which reflects light from the transmissive illumination source and illuminates the sample on the stage from above; (c) a transmissive illumination optical unit including at least the tilt mirror is disposed so as to move in a direction in which the transmissive illumination optical unit is brought away from the stage from a normal position; and (d) a sample cover for shielding a light from the stage, wherein the sample cover is displaceable so as to expose the stage.