1. An X-ray imaging apparatus comprising: a three-dimensional blood-vessel image collecting unit that collects a three-dimensional blood vessel image on which a blood vessel image is enhanced; an X-ray image collecting unit that collects an X-ray image; a composite-image creating unit that creates a three-dimensional projection image projected based on a state of the X-ray imaging apparatus from the three-dimensional blood vessel image collected by the three-dimensional blood-vessel image collecting unit, and creates a composite image of created three-dimensional projection image and the X-ray image collected by the X-ray image collecting unit; a displacement determining unit that determines a displacement between an aneurysm on the three-dimensional projection image and an aneurysm on the X-ray image; and a registration unit that registers the composite image created by the composite-image creating unit by using the displacement determined by the displacement determining unit, and displays registered composite image onto a display unit.