of the cam ring 24 as shown in fig7 three protruding sections 2406 projecting radially and outwardly are provided on the rear end of the cam ring 24 in such a way as to be spaced in the circumferential direction thereof as shown in fig5 further during a state in which these three protruding sections 2406 engage with the cam grooves 2002 and 2004 of the fixed ring 20 the cam ring 24 performs rotational motions with respect to the fixed ring 20 so that these three protruding sections 2406 are moved along the cam grooves 2002 and 2004 consequently the cam ring 24 is moved in the direction of the optical axis thereof furthermore at least one of the cam grooves 2002 of the fixed ring 20 penetrates therethrough an end of an arm not shown provided on the protruding portion 2406 of the cam ring 24 which corresponds to the cam groove 2002 penetrating therethrough engages with the rectilinear groove 2205 of the rotative ring 22 through the cam grooves 2002 consequently the cam ring 24 and the rotative ring 22 are connected to each other and rotate with respect to the fixed ring 20 in other words when the rotative ring 22 is rotated the cam ring 24 moves in the direction of the optical axis while rotating the rectilinear guide ring 26 is provided in the radially inner portion of the cam ring 24 in such a manner as to be unable to rotate and as to move in the direction of the optical axis by being connected to the cam ring 24 particularly three protruding sections 2602 projecting radially and outwardly are provided on the rear end of the rectilinear guide ring 26 are provided by being spaced in the circumferential direction further.