In this short paper, the meaning of volcano observation of physical parameters relating with volcanic phenomena is summerized with respect of change of elastic parameters, change of potentials such as gravity and geomagnetic and observation of fluid motion. The substantial problems on volcanic phenomena are enumerated and discussions are made, among them, on 1) observation for the study of the deep and shallow structures of volcanoes and 2) observation for the study of the mechanism of eruptions. Modernization of observation techniques is also described itemizing in seismic, ground deformation, gravity, geomagnetic, geothermic and others. In accordance with the prediction of volcanic eruptions, the national project of the prediction of volcanic eruptions in Japan which started in 1949 is described.