To provide a measuring method, for a machine height, in which the high-accuracy machine height from the reference point of a surveying instrument can be obtained.

A reflecting-mirror unit 30 is attached to the tip of a telescope 22 at a surveying instrument 20. A reflecting mirror 32 which is tilted by an angle θ with reference to an optical axis is attached to the reflecting-mirror unit 30. The deflection angle γ of the telescope 22 when a reference point P is collimated via the reflecting mirror 32 from the telescope 22 is measured by an angle measuring device which is installed at the inside of the surveying instrument 20. A machine height H is found by means of trigonometry on the basis of the angle θ, on the basis of the deflection angle γ and on the basis of the distance (a) up to the reflecting mirror 32 from the center of the surveying instrument 20.