A measuring system, comprising a surveying instrument for projecting a laser beam by rotary irradiation and a photodetection sensor device installed at a measuring point, wherein the surveying instrument comprises a first radio communication unit, the photodetection sensor device comprises a second radio communication unit, and communication can be performed between the surveying instrument and the photodetection sensor device, wherein the surveying instrument comprises an angle detecting means for detecting a horizontal angle in a projecting direction of the laser beam and a first arithmetic unit for controlling the angle detecting means based on a receiving signal from the first radio communication unit, and the photodetection sensor device comprises a photodetection unit for receiving the laser beam and a second arithmetic unit for performing transmission of a photodetection notifying signal to notify the receiving of the laser beam by the photodetection unit and also for performing transmission of a synchronization data by the second radio communication unit to the first radio communication unit, wherein the first arithmetic unit calculates a horizontal angle of the projection of the laser beam when the photodetection sensor device receives the laser beam based on the photodetection notifying signal and the synchronization data.