When a plurality of X-ray images in a time sequence is stored in an image data storing unit (25), a marker coordinate detecting unit (26a) detects coordinates of a stent marker in each X-ray image, and a motion vector calculating unit (26b) calculates, with coordinates of the stent marker detected in a first frame as reference coordinates, a motion vector of the coordinates of the stent marker detected in each X-ray image of a second and subsequent frames with respect to the reference coordinates. Then, a filter application range determining unit (26c) moves and determines an application range of a smoothing filter in each X-ray image based on the motion vector, and the filtered image generating unit (26d) generates a filtered image by performing a process by the smoothing filter between application ranges determined in a process target image and a reference image.