A scanning microscope includes an objective lens for focusing illumination light onto a specimen; a scanning device for deflecting and scanning the illumination light; a pupil-projection optical system for illuminating a pupil of the objective lens with the scanned illumination light; and a total-magnification specifying unit for specifying a total magnification. An optical-system selecting unit changes at least one of the objective lens and the pupil-projection optical system such that a magnification of an optical system including the objective lens and the pupil-projection optical system is equal to or less than the total magnification specified by the total-magnification specifying unit and that the numerical aperture of the optical system is maximized. A deflection-angle determination unit determines a deflection angle of the illumination light deflected by the scanning device based on the ratio of the magnification of the optical system to the total magnification to achieve the total magnification.