The invention provides a surveying instrument, comprising a frame unit rotatable in a horizontal direction, a telescope unit as mounted rotatably in a vertical direction on the frame unit and further for sighting an object to be measured, a horizontal driving unit for rotating and driving the frame unit in a horizontal direction, a vertical driving unit for rotating the telescope unit in a vertical direction, a horizontal angle measuring unit for detecting a horizontal angle of the frame unit, a vertical angle measuring unit for detecting a vertical angle of the telescope unit and a control device, wherein the control device is adapted to calculate a solar altitude at a time moment by setting up coordinates of where the surveying instrument is installed and the time moment, and to make the telescope unit to set to the solar altitude as calculated by controlling the vertical driving unit, to control the horizontal driving unit, to execute searching of the sun by horizontally rotating the frame unit at the solar altitude as set up, to capture the sun, to sight the sun, to detect a horizontal angle under the sighted condition based on the horizontal angle measuring unit, and to survey a true north based on the horizontal angle as detected.