The present invention discloses a chuck mounted on a transmission shaft driven by a power source, and the chuck comprises a chuck body, plural jaws, a rear cap, an outer sleeve rotatablely fitted around the chuck body and located in front of the rear cap, and a transmission nut, characterized in that the chuck further comprises a drive pendulum support sleeve which is located between the outer sleeve and the transmission nut, connected with the outer sleeve and fitted around the chuck body; and a drive pendulum which is mounted on the drive pendulum support sleeve, swings between a first and second positions about its pivot axis, and has first and second drive portions, wherein the drive pendulum drives the transmission nut along a first transmission path through the first drive portion when it is in the first position, and drives the transmission nut along a second transmission path of more gripping force than the first transmission path through the second drive portion when it is in the second position. The present invention can provide greater gripping force, and is simple in structure and convenient in control.