the invention will be explained by referring to the accompanying drawings . according to the present invention , the maximum amount d of constriction of the spring 50 inside the optical fiber connector being less than double ( 2d ) of the constriction amount d is realized in practice as follows . as can be seen from fig2 a stopper step portion 34 is provided on the ferrule 30 , which stopper step portion 34 having a stopper surface facing against the bottom 42 of the connector sleeve 40 and the distance between the bottom surface 42 of the connector sleeve 40 and the distance between the bottom surface 42 of the connector sleeve 40 and the stopper step portion 34 is made equal to d , wherein ( d ≦ 2d ). by this arrangement , the ferrule 30 can not move backwardly relative to the connector sleeve more than the above distance d so that the spring 50 is not constrained more than the amount d . the ferrule 30 is in most of the cases formed as cylindrical shape or rectangular column shape provided with a fine hole for passing through the optical fiber along the center axis . in such a case of ferrule 30 , the stopper step portion 34 is preferably provided along the whole periphery of cylindrical shape or the like . however , even a part of the stopper step portion is lacked , as far as the function as a stopper is effective , such model may be included in the scope of the present invention . as can be seen from fig3 a stopper sleeve 62 is mounted on the ferrule 30 to rest between its flange 36 and the bottom 42 of the connector sleeve 40 so as to form a gap corresponding to the distance d (≦ 2d ) between the bottom 42 of the connector sleeve 40 . wherein the outer diameter of the stopper sleeve 62 is made smaller than the inner diameter of the coil spring 50 so as not to interfere the spring action of the coil spring 50 . in this embodiment , the stopper sleeve is fixed in its position against the ferrule 30 as shown in fig3 however , it functions properly as well as the case that the stopper sleeve is not fixed its position . accordingly , such embodiment of non - fixing the stopper sleeve is also included in the scope of the present invention . as can be seen from fig4 a stopper step portion 44 having the stopper surface against the flange 36 is provided near the bottom portion 42 of the connector sleeve 40 . the interval between the stopper step portion 44 and the flange 36 is made equal to the amount d (≦ 2d ). as can be seen from fig5 a stopper ring 64 formed of c - shape ring is mounted on the shaft of ferrule 30 and the interval between the stopper ring 64 and the bottom 42 of the connector sleeve 40 is made equal to d (≦ 2d ). in fig5 a groove is provided on the ferrule 30 to mate with the c - shape ring 64 and fixed it . but the invention is not limited to this construction . the necessary condition is to fix the stopper ring 64 not to move in axial direction of the ferrule 30 . accordingly , the stopper c - shape ring 64 may be fixed by using adhesive to the ferrule 30 . as can be seen from fig6 when the ferrule 30 moved backwardly against the bottom surface of the connector sleeve 40 in a distance corresponding to d (≦ 2d ), the spring 50 is fully constrained so that the ferrule can not move further backwardly . namely , this embodiment can be realized by arranging and selecting the height of the spring 50 when it is fully constrained and all the spring wire elements come in contact with each other so as not allow further constriction , to be related to said maximum amount d . in practice , this can be realized by selecting the height of the compressing spring 50 at its fully constrained condition , to be equal to an amount of the distance between the bottom 42 of the sleeve 40 and the flange 36 deducted by the distance d . in the foregoing explanation , no particular consideration has been made for the distance e between the flange 36 of the ferrule 30 and the adaptor 60 as shown in fig8 a , 8b and others , and an assumption was made as : in such a case , as can be seen from fig9 a , when the optical fiber cord 20a is moved backwardly , and if the ferrule 30 moves a distance more than amount e , a gap 32 may be produced between the ferrule 30b even the amount of movement is less than d . accordingly , when the designing the construction and for the setting of the condition d , the above situation should be taken into effect .