A Raman microscope constructed as a confocal optical scanning system wherein it comprises: a laser light source; an objective lens that concentrates a light beam from the laser light source and applies the concentrated light beam onto a sample; scanning means for moving a position of the light beam relatively with respect to the sample and thereby scanning a spot position of the light beam on the sample; light branching means for separating, among the light beam incident on the sample, outgoing light emitted from the sample toward the objective lens side from the light beam emitted from the laser light source and incident on the sample, the outgoing light being emitted with a different wavelength; a spectroscope that spatially disperses the outgoing light separated by the light branch means according to a wavelength; a 2D array photodetector that comprises light-receiving pixels arranged in an array and detects the outgoing light dispersed by the spectroscope; light restricting means disposed on an incoming side of the spectroscope, a plurality of light-passage sections being arranged along a direction perpendicular to a dispersing direction of the spectroscope in the light restricting means, the plurality of light-passage sections being adapted to allow concentrated outgoing light separated from the light beam by the light branching means to pass therethrough to the spectroscope side; and a lens that concentrates the outgoing light separated from the light beam by the light branching means onto the light restricting means; wherein the plurality of light-passage sections are formed so that the outgoing light beams that have passed through adjacent light-passage sections do not overlap each other on a light-receiving surface of the 2D array photodetector; wherein the outgoing light that has passed through one light-passage section is incident on N pixels in the direction perpendicular to the dispersing direction of the 2D array photodetector; and wherein the N pixels are added up; and wherein a size of the light-passage sections is configured to be adjustable in a direction in parallel with the dispersing direction while maintaining a constant size in the direction perpendicular to the dispersing direction. a laser light source; an objective lens that concentrates a light beam from the laser light source and applies the concentrated light beam onto a sample; scanning means for moving a position of the light beam relatively with respect to the sample and thereby scanning a spot position of the light beam on the sample; light branching means for separating, among the light beam incident on the sample, outgoing light emitted from the sample toward the objective lens side from the light beam emitted from the laser light source and incident on the sample, the outgoing light being emitted with a different wavelength; a spectroscope that spatially disperses the outgoing light separated by the light branch means according to a wavelength; a 2D array photodetector that comprises light-receiving pixels arranged in an array and detects the outgoing light dispersed by the spectroscope; light restricting means disposed on an incoming side of the spectroscope, a plurality of light-passage sections being arranged along a direction perpendicular to a dispersing direction of the spectroscope in the light restricting means, the plurality of light-passage sections being adapted to allow concentrated outgoing light separated from the light beam by the light branching means to pass therethrough to the spectroscope side; and a lens that concentrates the outgoing light separated from the light beam by the light branching means onto the light restricting means; wherein the plurality of light-passage sections are formed so that the outgoing light beams that have passed through adjacent light-passage sections do not overlap each other on a light-receiving surface of the 2D array photodetector; wherein the outgoing light that has passed through one light-passage section is incident on N pixels in the direction perpendicular to the dispersing direction of the 2D array photodetector; and wherein the N pixels are added up; and wherein a size of the light-passage sections is configured to be adjustable in a direction in parallel with the dispersing direction while maintaining a constant size in the direction perpendicular to the dispersing direction.