the base of the switch button 11 is normally abutted against the upper surfaces of cuts 7 and 8 which are formed on both sides of the base of the switch button 11 so that a space namely a click groove 9 corresponding to the minimum manual aperture value mark is provided between the side wall of the cut 7 and the side wall of the switch pin 13 another space namely a click groove 10 corresponding to the 34 a 34 mark is provided between the side wall of the cut 8 and the side wall of the switch pin 13 a click ball 17 is urged outwardly by a click spring 15 fixedly secured to the stationary ring 2 so that is is engaged with the click grooves 9 and 10 to click stop the aperture preset ring 6 the coupling ring 3 is provided with relief grooves 3a and 3b in which click springs 14 and 15 are freely movable an aperture rotation screw 5 fig2 is fixedly secured to the aperture rotation ring 4 the screw 5 extends through an elongated groove 2a formed in the stationary ring 2 and is engaged with a groove 6e in the aperture preset ring 6 the length of the elongated groove 2a corresponds to the maximum rotational angle of the aperture preset ring 6 rotation of the aperture preset ring 6 is stopped when the screw abuts against the end 2b of the elongated groove 2a when the click ball 16 is engaged with any one of the click grooves 6a by turning the aperture preset ring 6 counterclockwise as viewed in fig2 the aperture preset ring 6 is click.