Since 1995, the Communications Research Laboratory has been monitoring crustal deformation in the Tokyo metroplitan area using a compact VLBI network consisting of four fixed stations. This network is called the Key Stone Project (KSP) VLBI network. In 1997 the so-called "real-time'" VLBI technique was installed in the KSP VLBI network. Continuous improvement both in system hardware and in the observation method have resulted in a remarkable improvement in measurement accuracy. The accuracies in terms of the repeatability of measured station positions, at the present time, are 2.4 mm for the horizontal component and 12.3 mm for the vertical component.