This paper presents a realization of our IP based realtime VLBI (Very Long Baseline Interferometer) observation testbed with the highest sensitivity in the world. Today's rapid deployment of high-speed wide area networks will give a major breakthrough in VLBI astronomy in terms of its observational sensitivity and immediateness. VLBI requires huge amount of data transfer from several radio telescopes located separately each other for calculating cross-correlation. High-speed networks can be applied to such data transfer instead of conventional magnetical tape recording and physical transportation, which cause a serious performance bottleneck. We have newly designed and implemented a special component named gigabit network access node, which can exchange 2.048 Gbps telescope data through a 2.488 Gbps OC-48c/STM-16c SONET/SDH link. We have also constructed the world's first multi-gigabit-rate VLBI observation testbed using actual high-speed wide area optical networks and successfully conducted several real observations.