plurality of angles to measure the center position of the target ball 14 the difference vector of the measurement value in the center position with respect to the command value under this measuring condition can be decomposed into three components of the radial direction the axial direction and the tangential direction of the indexing axis these respective components can be approximated by a least squares method as an arc having errors such as fourier series of a zero order component a radius error a first order component a center deviation and a second order component an elliptical shape a radial direction component drr i an axial direction component dra i and a tangential direction component drt i of the measurement value in the k th indexing angle u03b8 ijk of the j th rotation axis under a measuring condition i can be expressed as formula 7 below drr i ra 0 i ra 1 i cos u03b8 ijk rb 1 i cos u03b8 ijk ra 2 i cos 2 u03b8 ijk rb 2 i sin 2 u03b8 ijk dra i aa 0 i aa 1 i cos u03b8 ijk ab 1 i cos u03b8 ijk aa 2 i cos 2 u03b8 ijk ab 2 i sin 2 u03b8 ijk drt i ta 0 i ta 1 i cos u03b8 ijk tb 1 i cos u03b8 ijk ta 2 i cos 2 u03b8 ijk tb 2 i sin 2 u03b8 ijk formula 7 here in a geometric error existing in the multi axis machine tool 1 assume that the perpendicularity between the x and y axes is dcxy the perpendicularity between the y and z axes is daxz the perpendicularity between the z and x axes is dbxz.