This actuating member (5) comprises:a push/pull member (30) which includesa first moving part (31) and second moving part (32) which are positioned on the base end-side of the long member (10) and which can move relative to one another in the axial direction of the long member (10), a first stretched part (33) that is stretched from the first moving part (31) to the tip-side of the long member (10), and a second stretched part (34) that is stretched from the second moving part (32) to the tip-side of the long member (10), the push/pull member being pushed/pulled in the axial direction of the long member (10) in conjunction with the movement of the moving parts (31, 32) a control member (40) which controls the movement of the moving parts (31, 32) and an advancing member (70) which is equipped with a reduced-width part (71), the width of which is gradually reduced towards the tip, the advancing member (70) advancing in between the first moving part (31) and the second moving part (32), moving the moving parts (31, 32), in accordance with the operation of the control member (40).Élément dactionnement (5) qui est équipé dun élément de traction-poussée (30) comprenant une première partie mobile (31) et une seconde partie mobile (32) positionnées sur le côté terminal de base dun élément allongé (10) et pouvant se déplacer lune par rapport à lautre dans la direction axiale de lélément allongé (10), une première partie allongée (33) qui sétend de la première partie mobile (31) à la pointe de lélément allongé (10), et une seconde partie allongée (34) qui sétend de la seconde partie mobile (32) à la pointe de lélément allongé (10), lélément de traction-poussée étant poussé/tiré dans la direction axiale de lélément allongé (10) en conjonction avec le mouvement des parties mobiles (31, 32), dun élément de commande (40) qui commande le mouvement des parties mobiles (31, 32), et dun élément davance (70) qui est pourvu dune partie à largeur réduite (71) dont la largeur rétrécit g
