In an electron particle machine for observing, inspecting, processing or analyzing a semiconductor wafer as a substrate or a sample, a light source is installed in a preparation chamber. A chucking stage for chucking the semiconductor wafer with a chuck using static electricity is provided with parts for connecting to earth such that they are in contact with the chucked semiconductor wafer. After the chuck using static electricity is released after observation, inspection, process or analysis, a surface of the semiconductor wafer and the parts for connecting to earth are irradiated with light from the light source. This provides conductivity to the surface of the semiconductor wafer, so that charge accumulated on the semiconductor wafer is removed from the surface through the parts for connecting to earth.