It is an object to provide a diffusion weighted image processing apparatus or the like which can correct a distortion of a diffusion weighted image requiring smaller endurance on a patient in a diffusion weighted image processing method for correcting distortion of a diffusion weighted image. The diffusion weighted image processing apparatus has a correcting device which relatively corrects, with mutual reference among two or more diffusion weighted images having different directions of gradient field pulses during imaging, distortions occurring in the directions of the gradient field pulses during the imaging of the diffusion weighted images, the distortion being caused by the gradient field pulse of the diffusion weighted image.