| 摘要 |
PROBLEM TO BE SOLVED: To obtain an electron beam correction device which can surely perform fastening and loosening operation of a ring-shaped magnet to a holder. SOLUTION: A ring-shaped magnet 64 is mounted to a holder 12 with a big hole part 13 and a nail part 15, a lock ring with a fastening surface part 16a which contacts with the nail part 15, is formed so as to be mounted between the nail part 15 and the ring-shaped magnet 64, further, it is so constituted that the nail part does not slip out from the fastening surface of the lock ring by engaging the lock ring with the nail part by an engaging means restricting the displacement of the nail part in radial direction.
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