Surveying instrument

A surveying instrument including an instrument height measuring unit configured to make a distance measurement by irradiating light toward a position below a vertical axis of a surveying instrument main body, and calculate an instrument height, wherein

• the instrument height measuring unit comprises:
• a light transmitting unit configured to emit light;
• a beam splitter configured to be incident with light emitted from the light transmitting unit, split the incident light into reference light and distance-measuring light, send the reference light to a reference light path, and send the distance-measuring light to a distance-measuring light path;
• a first light receiving unit configured to receive the reference light;
• a second light receiving unit configured to receive light being the distance-measuring light that has been emitted toward a position below the vertical axis of the surveying instrument main body and returned by being reflected by a distance-measuring object;
• and
• an arithmetic unit configured to calculate the instrument height based on light reception signals generated by the first light receiving unit and the second light receiving unit,
• wherein the first and second light receiving units receive light from the same light transmitting unit.