The proxy mechanism widely used in WWW systems offers low-delay and scalable delivery of data by means of a "proxy server". By applying proxy mechanism to video streaming systems, high-quality and low-delay video distribution can be accomplished without imposing extra load on the system. We have proposed proxy caching mechanisms to accomplish the high-quality and highly-interactive video streaming services. In our proposed mechanisms, proxies communicate with each other, retrieve a missing video data from an appropriate server by taking into account transfer delay and offerable quality. In addition, the quality of cached video data can be adapted appropriately in the proxy to cope with the client-to-client heterogeneity, in terms of the available bandwidth, end-system performance, and user preferences on the perceived video quality. In this paper, to verify the practicality of our mechanisms, we implemented them on a real system for MPEG-4 video streaming services, and conducted experiments. Through evaluations, it was shown that our proxy caching system can provide users with a continuous and high-quality video distribution in accordance with network condition.