To provide an image processing apparatus suitable for simplifying and accelerating a filtering process at the time of decoding an image and implementing an effective filter effect. A deblock filtering process judges whether or not difference values between values of subject pixels v.sub.0 to v.sub.7 and values of reference pixels r.sub.y0 to r.sub.y7 are exceeding a threshold, performs horizontal filter operation as to the subject pixels v.sub.0 to v.sub.7 based solely on the values of the subject pixels v.sub.0 to v.sub.7 and the values of the reference pixels r.sub.x0 and r.sub.x1, determines whether or not to perform vertical filter operation as to the subject pixels v.sub.0 to v.sub.7 based solely on the judgment result, and performs the vertical filter operation as to the subject pixels v.sub.0 to v.sub.7 based solely on the values of the subject pixels v.sub.0 to v.sub.7 and the values of the reference pixels r.sub.y0 to r.sub.y7.