The optical system of the microscope includes a close-up optical system that faces an object, a pair of imaging optical systems that take object light rays passing through regions of the close-up optical system, and an illuminating optical system that guides illumination light emitted from a light source to illuminate the object. Each lens included in the close-up optical system has a semicircular shape in which one side is cut out. The close-up optical system is held in a first lens barrel, and the illuminating optical system is held in a second lens barrel. The second lens barrel is arranged in the cutout space of the close-up optical system inside the first lens barrel. A light shielding member is attached to the second lens barrel to prevent a leak of the illumination light through grooves formed on the second lens barrel.