We describe a multi-station system dedicated to measurements of the solar wind plasma using the interplanetary scintillation technique. The observation system, which is operated at a frequency of 327 MHz, consists of four stations located at Toyokawa, Fuji, Sugadaira and Kiso. The newest station was constructed at Kiso in 1993 to make a four-station system. The present system, however, has insufficient sensitivity to measure enough IPS sources for observing the solar wind with good spatial and temporal resolution. As a result, for example, one synoptic map of solar wind speeds requires the superposition of data for three solar rotations. Therefore we have begun the project to upgrade the antenna system at each station. To start with, the Fuji antenna has successfully been improved with an optimum design of the primary feed system and the development of a low noise preamplifier. The Fuji antenna system after the improvement achieved the minimum detectable flux density of 0.3 Jy (bandwidth: 10 MHz, time constant: 100 ms) which is nearly five times better than the previous system. This upgrade project is expected to be fruitful during the coming decade for solar wind study.