A laser scanning device for measuring the distance to an object in a target area by projecting laser light scanningly is provided not only with a light receiving element for receiving reflected light from the target area to detect its intensity but also with an auxiliary light receiving element for receiving reflected light from a neighboring area which will be scanned next. The gain of amplifier for amplifying the intensity of light received by the light receiving element is adjusted based on the intensity of light received by the auxiliary light receiving element so as to avoid saturation. A one-dimensional or two-dimensional light receiving element for simultaneously receiving reflected light from a plurality of areas including the target area may be used instead.