1. An X-ray inspection apparatus, comprising: an X-ray generator provided with an X-ray detector having a point-shaped tube focal spot, the X-ray detector generating an X-ray beam from the tube focal spot, the X-ray beam having a given cone angle in a scan direction and a predetermined fan angle in a direction which is along a section perpendicular to the scan direction; an X-ray detector provided with a plurality of pixels two-dimensionally arrayed and configured to output at a predetermined frame rate frame data presenting strength of the X-ray beam incident on the pixels; moving means for moving either a pair of the X-ray tube and the X-ray detector or the object relatively to the other in the scan direction, the X-ray detector being arranged to be opposed and separated to and from the X-ray tube with a space provided therebetween, an object being inspected being positioned in the space, wherein either the pair of the X-ray tube and the X-ray detector or the object is moved such that a center line of the X-ray beam in a width direction thereof crosses with each of a plurality of tomographic planes virtually set in the space and parallel to the scan direction, a crossing length in each of the tomographic planes being always constant; data acquiring means for acquiring the frame data outputted from the X-ray detector, while the moving means move the pair of the X-ray tube and the X-ray detector or the object relatively to the other; frame data generating means for generating, based on the frame data, frame data of each of the plurality of tomographic planes depending on a spread of the fan-shaped X-ray beam and positional differences of the plurality of tomographic planes in a perpendicular direction to the tomographic planes; tomographic image generating means for generating tomographic images of the tomographic planes by applying a laminography method to the frame data of the tomographic planes, generated by the frame data generating means; edge information generating means for generating a three-dimensional distribution of edge information based on calculating, every pixel of each of the tomographic images, edge information showing changes in pixel values of the respective tomographic images generated by the tomographic image generating means; and composite image generating means for generating a single composite image through searching every pixel the three-dimensional distribution of the edge information in a direction passing through the tomographic planes to detect a pixel showing a maximum of the edge information, selecting, at a pixel positon corresponding to the detected pixel, only pixels of the tomographic images or other tomographic images generated from the tomographic images, and combining the selected pixels, the single composite image showing an inside state of the object.