Abstract: A strobo electron beam apparatus is provided having an energy analyzer, which: measures the voltage in the integrated circuit; samples a secondary electron signal by setting and connecting a retarding voltage of the energy analyzer to the measured phase; obtains the waveform of the secondary electron signal by a one time or several times phase scanning; and adds the product of a suitable coefficient and a difference between the secondary electron signal waveform, and a slice level to the retarding voltage and corrects the same. Multiple units are provided for: judging the conversion of the retarding voltage, from the value of the dispersion for the slice level of the secondary electron signal waveform; for adding and giving a mean of the retarding voltage, for obtaining a measured value of retarding voltage having a desired S/N ratio; and for random phase scanning so that the measured value having a desired S/N ratio can be easily obtained.