A microscope illumination device comprising: a light source; an objective for illuminating a specimen; a collector lens for converting light from the light source into parallel light; a fly-eye lens placed near to rear focal point of the collector lens; an epi-illumination projection lens for projecting light source images generated by the fly-eye lens onto the objective pupil; a tube lens for imaging an observation light from the objective; and a fluorescence cube placed between the objective and projection lens and comprised a filter, satisfies the expression γ2*ffly*D