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 supllying 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 on the basis of phases of the ultrasound echo signals acquired from the target by transmitting ultrasounds more than one time to a region of interest within the target.