For the purpose of determining an offset of the position of an X-ray tube
from a prespecified position, and correcting axially projected data D1 and
pixel projection data D2 based on the determined offset, proper axially
projected data D1 can be obtained by an X-ray focal spot 2102 and a
detector 2103 by determining axially projected data D1 at a point 2104
using projection data D0 obtained by a channel that detects an X-ray
emitted from the X-ray focal spot 2102 and passing through the point 2104,
and shifting the determined axially projected data D1 by a distance DIS1
in the (+)-direction of the x-axis.
