A circular knitting machine, comprising: - a needle-holding cylinder having a plurality of longitudinal grooves arranged around a central axis (X-X) of the needle-holding cylinder; - a plurality of needles, each being housed in a respective longitudinal groove; - actuating cams arranged around the needle-holding cylinder and movable with respect to said needle-holding cylinder around the central axis (X-X) for causing or allowing the movement of the needles along the longitudinal grooves so as to enable stitch formation by said needles; - a drive chain for each needle inserted into the respective longitudinal groove, located below the respective needle and operatively interposed between the respective needle and said actuating cams; wherein said drive chain comprises: a sub-needle arranged below the needle and engaged with the needle in order to be axially moved in the respective longitudinal groove together with said needle; wherein the sub-needle comprises a movable butt radially movable between an operating position, in which it is extracted from the needle-holding cylinder in order to be engaged with respective first paths defined by first actuating cams and cause the needle to be activated, and a non-operating position, in which it is retracted in the needle-holding cylinder in order to not be engaged with said first paths; a selector partly located below the sub-needle and partly alongside the sub-needle, wherein the selector is configured for oscillating between an active position and a rest position, so as to control a shifting of the movable butt between the operating position and the non-operating position; - at least one selecting device (36, 37) acting upon command on the selectors for controlling the passage thereof between the active position and the rest position; said machine being characterized in that it comprises a guide arranged around the needle-holding cylinder; wherein said needle-holding cylinder is movable with respect to the guide around the central axis (X-X); wherein a butt of the selector located at a lower end of said selector is engaged with the guide; wherein the guide is configured for blocking or releasing the oscillation of the selector according to the position of the selector around the rotation axis (X-X). - a needle-holding cylinder having a plurality of longitudinal grooves arranged around a central axis (X-X) of the needle-holding cylinder; - a plurality of needles, each being housed in a respective longitudinal groove; - actuating cams arranged around the needle-holding cylinder and movable with respect to said needle-holding cylinder around the central axis (X-X) for causing or allowing the movement of the needles along the longitudinal grooves so as to enable stitch formation by said needles; - a drive chain for each needle inserted into the respective longitudinal groove, located below the respective needle and operatively interposed between the respective needle and said actuating cams; wherein said drive chain comprises: a sub-needle arranged below the needle and engaged with the needle in order to be axially moved in the respective longitudinal groove together with said needle; wherein the sub-needle comprises a movable butt radially movable between an operating position, in which it is extracted from the needle-holding cylinder in order to be engaged with respective first paths defined by first actuating cams and cause the needle to be activated, and a non-operating position, in which it is retracted in the needle-holding cylinder in order to not be engaged with said first paths; a selector partly located below the sub-needle and partly alongside the sub-needle, wherein the selector is configured for oscillating between an active position and a rest position, so as to control a shifting of the movable butt between the operating position and the non-operating position; a sub-needle arranged below the needle and engaged with the needle in order to be axially moved in the respective longitudinal groove together with said needle; wherein the sub-needle comprises a movable butt radially movable between an operating position, in which it is extracted from the needle-holding cylinder in order to be engaged with respective first paths defined by first actuating cams and cause the needle to be activated, and a non-operating position, in which it is retracted in the needle-holding cylinder in order to not be engaged with said first paths; a selector partly located below the sub-needle and partly alongside the sub-needle, wherein the selector is configured for oscillating between an active position and a rest position, so as to control a shifting of the movable butt between the operating position and the non-operating position; - at least one selecting device (36, 37) acting upon command on the selectors for controlling the passage thereof between the active position and the rest position;