1. A displacement measurement apparatus comprising: a sensor for transmitting ultrasounds to a target in accordance with drive signals, and detecting ultrasound echo signals generated in the target to output echo signals; driving and processing means for supplying the drive signals to the sensor, and processing the echo signals outputted from the sensor; control means for controlling the driving and processing means; and data processing means for yielding a local 3D, 2D, or 1D displacement vector and/or local displacement vector components by solving simultaneous equations, coefficients of said simultaneous equations being expressed at each position by temporal change of a phase of the echo signal at the position and frequencies of the respective directions at the position derived by applying specified processing to complex analytic signals obtained from the echo signals acquired by transmitting ultrasounds more than one time to a region of interest within the target.