A microscope comprising an auto focus apparatus, the microscope comprising a camera and an observation optical system including an objective lens and an imaging lens for capturing a light emitted from an object by the camera via the objective lens, the auto focus apparatus comprising: a light source which irradiates an auxiliary light for focal point detection onto the object; an auto focus illumination optical system which forms an optical image of the auxiliary light from the light source on the object via the objective lens; an auto focus imaging optical system which forms an image of reflected auxiliary light reflected from the object via the objective lens; a photoelectric converter which is disposed in an imaging position of the reflected image by the auto focus imaging optical system, and detects the reflected image of the auxiliary light; a wavelength selection means, disposed on the common optical path of the auto focus illumination optical system, the auto focus imaging optical system, and the observation optical system; and irradiation optical path change means (135, 261), disposed on a common optical path of the auto focus illumination optical system and the auto focus imaging optical system, wherein the wavelength selection means is arranged to reflect the auxiliary light from the light source, to reflect the auxiliary light reflected from the object via the objective lens towards the irradiation optical path change means (135, 261) and to transmit light emitted by the object via the objective lens towards the imaging lens; the microscope being characterized by the irradiation path change means (135, 261) being operationally arranged for moving an irradiation position of the auxiliary light on the object to an area within an observation field of the objective lens and to an area outside an observation field of the camera. a light source which irradiates an auxiliary light for focal point detection onto the object; an auto focus illumination optical system which forms an optical image of the auxiliary light from the light source on the object via the objective lens; an auto focus imaging optical system which forms an image of reflected auxiliary light reflected from the object via the objective lens; a photoelectric converter which is disposed in an imaging position of the reflected image by the auto focus imaging optical system, and detects the reflected image of the auxiliary light; a wavelength selection means, disposed on the common optical path of the auto focus illumination optical system, the auto focus imaging optical system, and the observation optical system; and irradiation optical path change means (135, 261), disposed on a common optical path of the auto focus illumination optical system and the auto focus imaging optical system, wherein the wavelength selection means is arranged to reflect the auxiliary light from the light source, to reflect the auxiliary light reflected from the object via the objective lens towards the irradiation optical path change means (135, 261) and to transmit light emitted by the object via the objective lens towards the imaging lens; the microscope being characterized by the irradiation path change means (135, 261) being operationally arranged for moving an irradiation position of the auxiliary light on the object to an area within an observation field of the objective lens and to an area outside an observation field of the camera.