The eyepiece connecting device 20 includes a lock ball 24 pressed against the eyepiece 17, a stepped pipe 40 having a lock ball hole 41 in which the lock ball 24 is slidably disposed, a large diameter portion 40 b of the stepped pipe 40 A cam surface 36 which is rotatably mounted on a ring mounting surface 43 provided on the outer circumferential surface side of the main body 1 and is rotated in one direction to obtain a holding and fixing state while rotating in the other direction to obtain a mounting and detaching state The stepped pipe 40 has a convex piece having a flat surface 42 a which protrudes outwardly from the outer peripheral surface of the large diameter portion 40 b and sandwiches the rotary ring 30 with the ring placing surface 43 42, and the rotary ring 30 has an axial groove 34 through which the projecting piece 42 can pass, a sliding plane 33 on which one flat surface 42 a is slidably disposed, and a convex piece 42 which engages the axial groove 34 And restricting portions 23 and 35 for preventing falling out through the through holes.接眼部連結装置20は、アイピース17に押し当てられるロックボール24と、ロックボール24が摺動自在に配置されるロックボール孔41有する段付パイプ40と、段付パイプ40の太径部40bの外周面側に設けられたリング載置面43に回動自在に載置され、一方向に回転されて保持固定状態を得る一方、他方向に回転されて取り付け取り外し状態を得るカム面36を有する回転リング30と、を備え、段付パイプ40は、太径部40bの外周面から外方に突出しで、回転リング30をリング載置面43とで挟持する一平面42aを備えた凸片42を有し、回転リング30は、凸片42が通過可能な軸方向溝34、一平面42aが摺動自在に配置される摺動平面33、及び、凸片42が記軸方向溝34を介して脱落することを防止する規制部23、35、を有する。
