A trocar comprises a retention cannula comprising an inverted or incised retention pattern disposed thereon. The invention includes switching three diaphragm potentials during a transition from a filling phase to an acceleration phase in order to maintain a potential along the axis of the injected ion beam at a constant level, to prevent any penetration by the accelerating fields during the filling phase and to obtain extremely high mass resolution in the acceleration phase through a lens effect. The base maintains the position of the display device. A damper is coupled to one of the second pair of pulleys, which engages the pulley to rotate about an axis to damp the rotary motion of one of the second pair of pulleys in such a manner that the intermediate storage section is in tension during retraction and withdrawal. The first gas-permeable membrane, which is permeable to gas but impermeable to liquid, is disposed in the atmosphere communication hole.