Surveying instrument

A surveying instrument comprising a tripod which is installed on an installation surface and a surveying instrument main body which is provided on said tripod and laterally rotatable around a longitudinal axis, wherein said tripod includes a base module, a reference leg which is integral with said base module and has a known relationship between a lower end of said reference leg and a machine reference point which is a machine center of said surveying instrument main body, and two auxiliary legs, wherein said surveying instrument main body includes a distance measuring module configured to measure a distance to an object to be measured, a lateral rotation angle detector configured to detect a lateral rotation angle of said surveying instrument main body, and an arithmetic control module, said reference leg is installed in such a manner that a lower end of said reference leg coincides with a reference point, and said arithmetic control module configured to calculate a position of said machine reference point with respect to said reference point based on said positional relationship between said lower end of said reference leg and said machine reference point.