Surveying Apparatus

A surveying apparatus comprising, an observation optical system having an image sensor for outputting a digital image signal and a zoom optical system, a reference-pattern projection optical system for making a reference pattern enter said observation optical system in an infinity state and for forming an image on said image sensor, a rotation mechanism capable of rotating said observation optical system and said reference-pattern projection optical system integrally in two directions of horizontal and vertical, a horizontal angle detector and a vertical angle detector for detecting a horizontal angle and a vertical angle of rotation in the two directions of said rotation mechanism, and an arithmetic control unit, wherein said arithmetic control unit measures the horizontal angle and the vertical angle of a sighting point based on detection results of said horizontal angle detector and said vertical angle detector and based on a difference between said reference pattern on said image sensor and the sighting point of said observation optical system.