A calibration method of an X-ray measuring device includes: a front-stage feature position calculation step of parallelly moving spheres disposed in N places a plurality of times, and identifying centroid positions ImPos(1 to Q)_Dis(1 to M)_Sphr_(1 to N) of projected images of the spheres in the N places; an individual matrix calculation step of calculating an individual projection matrix PPj (j=1 to Q) for each of the spheres; an individual position calculation step of calculating moving positions Xb of the spheres on the basis of the individual projection matrix PPj (j=1 to Q); a coordinate integration step of calculating specific relative position intervals X(1 to N) of the spheres; a rear-stage feature position calculation step; a transformation matrix calculation step of calculating a projective transformation matrix Hk (k=1 to Q); a rotation detection step; a position calculation step; and a center position calculation step.