The invention provides a surveying instrument, which comprises a horizontal rotating unit, a measuring unit installed on the horizontal rotating unit, a coupler for mechanically coupling the horizontal rotating unit with the measuring unit, and a connector for electrically connecting the horizontal rotating unit with the measuring unit, wherein the coupler couples the horizontal rotating unit with the measuring unit and can separate from each other, the connector can electrically connect the horizontal rotating unit with the measuring unit and can separate from each other, wherein the horizontal rotating unit comprises a driving unit for rotating the measuring unit, a horizontal angle detector for detecting a horizontal angle, and a horizontal angle control unit for calculating horizontal angle data based on a signal from the horizontal angle detector and for controlling the driving unit, wherein the measuring unit comprises a distance measuring unit for performing a distance measurement, a vertical angle detector for detecting a vertical angle at a time of distance measurement, a vertical angle control unit for calculating vertical angle data based on detection results from the vertical angle detector, a coordinate calculating unit, and a main control unit, wherein the horizontal angle control unit transmits the horizontal angle data at the time of distance measurement to the coordinate calculating unit via the connector based on a control signal from the main control unit and distance measurement data by the distance measuring unit and the vertical angle data from the vertical angle control unit are inputted to the coordinate calculating unit, and the coordinate calculating unit is constituted so as to calculate three-dimensional data based on the horizontal angle data, the distance measurement data and the vertical angle data.