PURPOSE: To prevent the target point for observation on a specimen from dislocation off from the axis of an electron beam even though the shaft of a specimen holder is rotated, by mounting conical supporting rollers in the retention part which retains the specimen holder slidably in the axial direction.

CONSTITUTION: A specimen holder 3 under the retention surface for it of a retaining cylinder 4 is supported by a supporting part S slidably along the axis A, and the part S is fitted with conical supporting rollers 15 in positions symmetrical to the left and right under the retention surface. These supporting rollers 15 are arranged in the part S so that the cylindrical surface 16 of each supporting roller 15 contacts the outside surface of the holder 3 wherein the contacting point lies at the point 120deg. turned from vertical up the retaining cylinder 4. A pressure roller 11 supported by a bearing member 12 presses the holder 3 downward vertically from above with the aid of a spring mounted on the cylinder 4, and thereby the holder 3 is retained in a constant position. Even in the case the cylinder 4 and holder 3 are inclined, play in the target specimen position with the axis of electron beam is removed to lead to suppressing runoff of the image to possible minimum.