An X-ray apparatus includes a pixel-extracting section for extracting pixels determined in advance in each line of an image containing a grid moiré pattern, a FFT processing section for performing one-dimensional FFT to the extracted pixels, a peak-frequency detecting section for detecting a peak frequency from a frequency characteristic for each line having undergone FTT, a frequency-characteristic preparing section for preparing a frequency characteristic for extracting the grid moiré pattern in accordance with the detected peak-frequency, an inverse FFT processing section for performing inverse FFT to the frequency characteristic prepared by the frequency-characteristic preparing section, and an FIR filtering section for performing FIR filtering on the image with use of a value calculated by the inverse FFT processing section as an FIR filter coefficient.