An X-ray diagnostic apparatus includes a peak frequency detector detecting a peak frequency of a first harmonic in a moiré pattern of a grid appearing in an image； a first and second harmonic remover removing the first harmonic and a second harmonic in the moiré pattern from the image in accordance with the peak frequency of the first harmonic to obtain a first and second harmonic removed image； a third harmonic extracting-filter generating unit calculating a peak frequency of a third harmonic in the moiré pattern in accordance with the peak frequency of the first harmonic to generate a third harmonic extracting filter to extract the third harmonic； a third harmonic extracting unit extracting the third harmonic from the first and second harmonic removed image based on the third harmonic extracting filter and a third harmonic subtracting unit subtracting the extracted third harmonic from the first and second harmonic removed image to obtain a third harmonic removed image.
