A surveying system comprises an object to be measured having a retro-reflector and a surveying instrument main body for emitting a distance measuring light and performing a measurement based on a reflected distance measuring light, wherein the surveying instrument main body comprises a distance measuring light projecting module, a photodetector, a measuring unit, an optical axis deflector which has a reference optical axis and deflects a distance measuring optical axis, a projecting direction detecting module which detects a deflection angle and a deflection angle direction of the distance measuring optical axis, and an arithmetic control module, and wherein the arithmetic control module is configured to control the optical axis deflector, to perform a two-dimensional scan with the distance measuring light, to detect the deflection angle direction of the distance measuring light at a moment of detecting a photodetecting signal by the projecting direction detecting module, and to move an approximate center of the two-dimensional scan in the detected deflection angle direction.