We have built up a new apparatus of reflection high-energy electron diffraction system with two pairs of magnetic coils to measure rocking curves in short time. By using this system, we succeeded in the study of dynamic structure change during epitaxal growth of Si/Si(111). The system is also useful to study of surface structure under extreme conditions, because the measurement time is short. We have also applied it to analysis of surface structure at high temperature near the melting point, and discovered a new surface phase on the Si(111) surface.