1. An X-ray imaging apparatus having an X-ray irradiation unit to irradiate an X-ray and an imaging unit to capture an X-ray image based on the X-rays comprising: a first subtraction unit configured subtract a first X-ray image captured by the imaging unit from a second X-ray image captured by the imaging unit to generate a first subtraction image showing information on a blood vessel; a calculation unit configured to calculate an amount of pixel shift between the first X-ray image captured by the imaging unit and the third X-ray image captured by the imaging unit; a second subtraction unit configured to subtract the first X-ray image from the third X-ray image to generate a second subtraction image showing information on an insertion instrument, the first X-ray image being performed with a pixel shift correction based on the amount of pixel shift; and a synthetic unit configured to combine the first subtraction image with the second subtraction image to generate a synthetic image by performing the pixel shift correction based on the amount of pixel shift.