PURPOSE: To facilitate the handling of samples and obtain an X-ray microscope with a highly efficient X-ray optical system by providing a housing chamber whose degree of vacuum is lower than that inside a vacuum container to be provided.

CONSTITUTION: This microscope is structured by providing a partition 102 and a low-pressure sample chamber 100 sealed by an X-ray transmitting window 103 in a vacuum lens tube 6 and installing a sample capsule 104 of an open type in the chamber 100. Since the X-ray transmitting window 103 in the low- pressure sample chamber 100 has only to separate the low pressure in the sample chamber 100 from the vacuum in the vacuum lens tube 6, the differential pressure is little and the X-ray transmitting window 103 need not be very strong. Consequently, it is possible to use the thin X-ray transmitting window 103 with a good X-ray penetration. Moreover, the pressure in the low-pressure sample chamber 100 is required to be as much as or higher than such steam pressure as not to vaporize a culture solution for holding a sample 24. As the space of the low-pressure sample chamber 100 absorbs few X rays, the sample 24 can be observed in a highly efficient X-ray optical system.