1. A method of constructing multi tomographic image comprising: an X-ray source for irradiating X rays onto a subject, an X-ray imaging means for detecting X rays to pass through the subject, a swivel drive means for making an imaging system constituted by oppositely arranging and fixing the X-ray imaging means and the X-ray source at a certain distance, centered on the subject, a frame image storage means for storing image information being obtained by the X-ray imaging means as a frame image, therein, an image processing means for extracting the frame image from the frame image storage means, and for forming a panoramic image with digital processing, a large-capacity processed image storage means for storing the processed image, a whole image display and storing means for displaying and storing each tomographic image in the large-capacity processed image storage means, and an output means for outputting whole image of the whole image display and storing means, whereby in order to construct a multi-tomographic image, the frame image storing means is made to be a large-capacity frame image storage means, a certain frame image taken out of frame images stored in the large-capacity frame image storage means is projected to the value of each pixel at the radius place in the desire location along the X-ray transmission route at photographing as a square cell element of a near-circular arc displayed by polar coordinates, such a process is performed sequentially with respect to each X-ray photographed mage, by using the angle rotated while obtaining each X-ray photographed mage as a unit angle, the above processed respective X-ray photographed images are added sequentially by shifting every unit angle, and finally, a tomographic image is constructed at the radius place in the desire location.