A displacement measurement method for achieving, at each position of interest, high accuracy measurement of a displacement, a velocity and a strain in an actually generated beam direction by measuring the beam direction angle from ultrasound echo data. The method includes the steps of: generating an ultrasound echo data frame through scanning an object in a lateral direction with an ultrasound steered beam having one steering angle calculating both a beam direction and a frequency in the beam direction based on an azimuth angle φ=tan−1(fy/fx), a polar angle θ=cos−1[fz/(fx2+fy2+fz2)1/2], and a frequency (fx2+fy2+fz2)1/2 in the case where first spectral moments calculated from local ultrasound echo data at plural different temporal phases are expressed by a three-dimensional frequency vector (fx, fy, fz) and calculating a displacement component in the beam direction at each position of interest generated between plural different temporal phases.
