PURPOSE: To observe change with the elapse of time without receiving the size and thickness of a specimen regardless of energy of incident electron beam, by a method wherein a specimen is succeedingly irradiated with electron beam and X-rays generated from the specimen is detected.

CONSTITUTION: Electron beam from an electron gun 2 is converged by a converging lens 3 to irradiate a specimen 1. X-rays generated from the specimen are detected by an energy dispersing type X-ray detector 4 and converted to a pulse signal having a peak corresponding to a wavelength to be sent into a peak analyser 6 through an amplifier. The pulse line having a specific peak selected in the peak analyser 6 is sent to a counter 7 and counted for a short definite time to be stored in a register group 8 in time series. The stored count value is read to be sent to a display apparatus 9 and a differentiation circuit 10. The output of the register group represents the timewise change of the X-ray count number due to electron beam damage and passed through the differentiation circuit to exhibit the speed of crystal collapse.