An X-ray imaging apparatus which obtains an X-ray image, the apparatus includes: an imaging unit including a plurality of detecting elements adapted to convert X-rays generated by an X-ray generating apparatus which outputs or stops X-rays in accordance with an operation instruction into an image signal and an obtaining unit adapted to obtain an operation start timing of the X-ray generating apparatus based on an image signal output from the imaging unit and obtain a difference between a timing of an operation instruction to the X-ray generating apparatus and the operation start timing.
