PURPOSE: To prevent deterioration in a CT image by a method wherein an X-ray source or an X-ray detection means is moved by a moving means to correct movement as caused by a thermal expansion of the X-ray source to set the X-ray source and the X-ray detection means in an initial relative position.

CONSTITUTION: A moving means control section 8 picks up an electrical signal Vb detected and outputted with a sensitive part 14b of an auxiliary detection section 10b and an electrical signal Vd detected and outputted with a sensitive part 14d to control a moving means 4 so that an output difference therebetween is nullified. Subsequently, the moving means 4 moves an X-ray detector 10 in a direction of slicing under the control of a moving means control section 8 so that a sector X-ray beam 5 from an X-ray tube 3 always aligns the center of the X-ray detector 10. With an apparatus 1 thus arranged, even if an X-ray focus of the X-ray tube 3 moves in a direction of slicing by a thermal expansion, the X-ray tube 3 and the X-ray detector 10 can be maintained at an initial relative position relationship by the moving means 4 thereby obtaining a CT image better with limited generation of artifact regardless of continuous scanning.