The laser scanning microscope comprises an objective focusing a laser beam on a sample, and takes fluorescence or reflected light from the sample, optical scanning means for scanning the laser beam on the sample two-dimensionally, an acousto-optic device, arranged on an optical path of a fluorescence or a reflected light, which selects and deflects only a light beam with the wavelength which corresponds to incident fluorescence or the reflected light and a frequency of the applied high frequency voltage, optical detection means for detecting a light beam through the acousto-optic device, and frequency scanning means for switching and setting a frequency of a high frequency voltage applied to the acousto-optic device.