In a VP-SEM that uses gas multiplication induced within a low-vacuum sample chamber and uses a method of detecting a positive displacement current, a secondary electron detector for the VP-SEM that responds at high speed, which can acquire a TV-Scan rate image at a low cost while saving a space is provided. A secondary electron detector is formed by forming the electron supplying electrode and the detection electrode on the flexible thin film type substrate such as a polyimide film, etc., by an etching method. Thereby, the space can be saved while realizing low cost due to mass production. Further, the ion horizontally moving with respect to the surface of the secondary electron detector is detected and the ion moving in a vertical direction returned to the sample holder is not detected, making it possible to realize a high-speed response.