Through the present invention, the rotation angle of a pelvis is calculated from a simple frontal X-ray image without being affected by such factors as race, image downscaling, gonad protection, or intestinal gas. A pelvic rotation angle calculation device for calculating the rotation angle of a pelvis from a simple frontal X-ray image of the pelvis, the pelvic rotation angle calculation device having an X-ray image input means for inputting a simple frontal X-ray image, an anatomical landmark acquiring means for acquiring an anatomical landmark which is set in relation to the simple frontal X-ray image, and a computation means for calculating the rotation angle of the pelvis on the basis of the anatomical landmark, the anatomical landmark including at least a teardrop or an obturator foramen, and the computation means calculating the rotation angle of the pelvis on the basis of the seize or positional relationship of the anatomical landmark.
