1. A method of determining the direction of application of gradient magnetic field for the detection of diffusive motion, comprising the steps of: producing, by being based on data which is collected by sequential application of diffusive motion detecting gradient magnetic fields along at least two axes out of three orthogonal axes, at least two diffusion-weighted images which correspond to the application axes; composing an image from the diffusion-weighted images by allotting different display colors thereto; displaying the composed image or the intensity-inverted version thereof; and determining the direction of diffusive motion detecting gradient magnetic field to be applied for the measurement of the diffusion coefficient of a region of interest on the composed image or the intensity-inverted image based on the hue of the region of interest.