In the detecting system for irradiating the electron beam and detecting the secondary electron thereof, an area of the detector is an important factor for high-speed detection. For the technique of the current electron optical system and detector, a detector of the area larger than a constant area is necessary and detection of 200 Msps or more by receiving limitation on the frequency inversely proportional to the area is substantially difficult. For example, for detection at 400 Msps under the condition that the required area is 4 mm square and the rate for 4 mm square is defined as 150 Msps, four discrete high-speed detectors of 2 mm square are arranged to amplify and then add the signals for A/D conversion. Otherwise, the secondary electron is sequentially inputted to the detector of 8 mm square with the secondary electron deflector, the secondary electron is detected at 100 Msps and arranged after the A/D conversion. In any case, the area of 4 mm square and rate of 400 Msps can be attained.