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 in an image； a 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 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 harmonic extracting filter to extract the third harmonic； a harmonic extracting unit extracting the third harmonic from the first and second harmonic removed image based on the harmonic extracting filter； and a harmonic subtracting unit subtracting the extracted third harmonic from the first and second harmonic removed image to obtain a third harmonic removed image.
