A radiation imaging apparatus comprises display means for displaying an image obtained by imaging an object and light projection means for projecting a light projection mark onto the object, and displays a light projection position on the object onto which the light projection mark is projected on the image. The light projection mark is projected as a line of intersection which is perpendicular to the surface of a detector and at which two planar flat light beams visually intersect each other, and the light projection position on the image is moved according to the movements of the flat light beams. By calculating projected lines obtained by projecting the light projection lines projected onto the object by the flat light beams onto the surface and displaying the projected lines on the image, the light projection position is displayed as a point of intersection of the projected lines on the image.