We have developed real-time VLBI systems, they use high-speed ATM (asynchronous transfer mode) networks. In these real-time systems, observed VLBI data is transmitted through ATM communication networks [STM-16 and STM-1] instead of being recorded onto magnetic tape. The STM-16 system was specially designed for the Key Stone Project (KSP), which is concerned with measuring crustal deformation using four stations in the Tokyo metropolitan area in Japan. CRL has also developed an lower bits rate ATM system (STM-1: 155.6 Mbps) for international real-time VLBI experiments. Cross-correlation processing and data observation are carried out simultaneously. With the real-time VLBI system, one operator can handle both the observation and the correlation processing. The systems were designed to enable automated operation throughout the entire process. We carried out real-time 24-hour VLBI experiments between Koganei and Kashima using the STM-1 ATM network, horizontal position uncertainty of about 3 mm and vertical position uncertainty of about 10 mm have been achieved.