An accurate real-time measurement of a displacement vector is achieved on the basis of the proper beamforming that require a short time for obtaining one echo data frame without suffering affections by a tissue motion. The displacement measurement method includes the steps of: (a) yielding ultrasound echo data frames by scanning an object laterally or elevationally using an ultrasound beam steered electrically and/or mechanically with a single steering angle over an arbitrary three-dimensional orthogonal coordinate system involving existence of three axes of a depth direction, a lateral direction, and an elevational direction and (b) calculating a displacement vector distribution by implementing a block matching on the predetermined ultrasound echo data frames yielded at more than two phases.
