This paper describes the possibilities of measuring deformation of machine tool components based on monitoring change in the optical beam path. Deformation is evaluated relatively between an optical beam source and a sensing element. The great advantage lies in the fact that an active sensing element can be replaced by a passive optical element. No electronics needs to be installed in the measured place. Thus there is no necessity to protect electronic elements in a harsh environment. Another advantage is no need for statically arranged cables when measuring deformation on moving components. The measuring equipment presented in this paper consists of a measuring part and a part for measuring the motion of the reference beam. The position of a stiff body in space is clearly defined by 6 coordinates. The described optical equipment enables measurement of 4 coordinates, or 5 coordinates if an interferometer is used. The unmeasured coordinate describes the rotation of the measured body around the axis parallel with the optical beam.