1. A frame rate converting method comprising the steps of: (a) estimating a plurality of bi-directional motion vectors using motion vectors determined from a current frame and a previous frame; (b) determining an estimated bi-directional motion vector from step (a), corresponding to a neighboring block, that has the minimum error distortion from among the plurality of motion vectors estimated in step (a); (c) setting a motion vector of a current block to be the estimated bi-directional motion vector determined in step (b); and (d) forming a frame to be interpolated with the motion vector set in step (c).