1. A method for analyzing motion of an imaging target by means of tagged MR images, the method comprising the steps of: performing, on the same motion of an imaging target, N L (N L : positive integer not less than 2) times of cine imaging by means of different tag patterns, to obtain N L pieces of time-series tagged MR images taken for a plurality of time phases in the motion of the imaging target; arranging N L pieces of pixel values of the same pixel in the N L pieces of tagged MR images at each time phase into a pixel value sequence having a length N L for the corresponding pixel; and analyzing the motion of the imaging target in the time-series tagged MR images by detecting pixels whose pixel value sequences constitute the same code sequence in different time phases, wherein each of the tag patterns is formed such that the pixel value sequence constitutes a predetermined code sequence, and wherein the step of analyzing motion of the imaging target in the time-series tagged MR images by detecting pixels includes at least calculating an amount of motion of the imaging target in a region less than the size of one pixel.