A chuck body is made up of axially movable plungers and jaws, in which the jaw has a master jaw body obliquely arranged with respect to an axis of the chuck body, the jaw also has a front face of the master jaw body and a rear end face of a master jaw head for restricting a position of the jaw with respect to the chuck body, a plunger receives a bushing which acts as a wedge means cooperating with the master jaw body, a driver at a rear end of the master jaw body being restricted in a backward movement within a range of a gap δ, and a wedge having a structure of canceling a moment applied to the jaw as a result of clamping, the driver providing a reactant force to the master jaw body for canceling a drawing force applied to a plunger.