A scanning optical microscope includes a light source, a light converging optical system, a stage, a scanning unit which displaces an illumination light and the stage relatively, a detecting optical system, and a photodetector. A light modulation element and a relay optical system are disposed on the light converging optical system side of the light source, and a modulated signal having only amplitude changed is input to the light modulation element, and the light modulation element is positioned such that the illumination light emerged from the light modulation element with respect to the modulated signal of a predetermined amplitude coincides with an optical axis of the light converging optical system, and a position of a pupil of the light converging optical system and a position of the light modulation element are conjugate through at least the relay optical system.