given of a closing motion of the barrier blades 5 and 6 in the lens barrier mechanism in fig1 the barrier driving ring 4 is fitted onto sliding portions la formed in the lens barrel 1 the inner circumferential surfaces 4 a of the barrier driving ring 4 are slidable on the outer circumferential surfaces of the sliding portions 1 a and therefore the barrier driving ring 4 can be smoothly rotated with respect to the lens barrel 1 in fig2 the barrier driving ring 4 has a cam 4 b used to convert the inward and outward motion of the lens barrel will respect to the camera body into the rotational motion of the barrier driving ring 4 the straight movement guiding member 2 has a contact portion 2 a brought into contact with the cam 4 b of the barrier driving ring 4 when a power source of the camera provided with the lens barrel of this embodiment is turned off the lens barrel 1 begins to be moved in to a predetermined collapse position in the camera body and thereby a relative distance between the straight movement guiding member 2 and the barrier driving ring 4 becomes short thereafter when the cam 4 b of the barrier driving ring 4 is brought into contact with the contact portion 2 a of the straight movement guiding member 2 the barrier driving ring 4 rotates in the direction of arrow u201c a u201d shown in fig2 as shown in fig3 the barrier driving ring 4 rotates in.