Quantitative shear wave velocity measurement inside the living tissue is a key technology in future qualitative diagnosis of breast tumor or liver diseases. We develop a novel shear wave velocity measurement system by using running wave number spectrum analysis of the complex displacement of the shear wave propagation excited by a single frequency. The velocity estimation method is demonstrated through the phantom experiments with the developed shear wave displacement measurement system. The validity of the measurement system is demonstrated by comparing with elastic wave simulation results. From the phantom experiments, it is shown that this method has high accuracy of velocity measurement even in the presence of large reflected waves.