A chuck structure that is configured to chuck an annular workpiece from a radially outer side of the workpiece and is arranged on a first vertically-movable shaft and a second vertically-movable shaft that are mounted to a rotary spindle, in response to the rotary spindle rotating about an axial center thereof, the first vertically-movable shaft and the second vertically-movable shaft being rotated in synchronization with the rotary spindle, and the first vertically-movable shaft and the second vertically-movable shaft being configured to be vertically moved independently of each other, the chuck structure comprising: leaf spring members arranged at a predetermined pitch along a circumferential direction of the chuck structure so as to be symmetrical with respect to a mechanism center axis; chuck claw members mounted to distal ends of the leaf spring members, respectively; and a pressing force applying mechanism configured to apply a force of pressing the leaf spring members radially inward, to thereby elastically press the chuck claw members onto a radially outer surface (Wa) of the workpiece, wherein in a free state, each of the leaf spring members extends straight and is arranged in an oblique posture so that a distal end side of each of the leaf spring members is directed radially outward, wherein the pressing force applying mechanism comprises a pressing member formed of a round bar with a small length, wherein the pressing member is held in contact with a radially outer side of each of the leaf spring members in the free state, in which each of the leaf spring members extends straight, wherein under a state, in which the pressing member is arranged so that an axis thereof is parallel to a direction orthogonal to an axis of the first vertically-movable shaft and an axis of the second vertically-movable shaft, the pressing member is held on a holding frame body mounted to the second vertically-movable shaft, wherein the pressing member is moved up and down with respect to the first vertically-movable shaft, wherein the holding frame body comprises a ring body and a fixed portion fixed to an upper surface of the second vertically-movable shaft with a bolt member, and wherein under a state in which the pressing member is held in contact with the radially outer side of each of the leaf spring members, in response to the ring body raised with respect to the leaf spring members, the pressing member is raised to press a center portion of the leaf spring members in a length direction of the leaf spring members to a distal end boss section side of the first vertically-movable shaft, by which the leaf spring members are pressed radially inward and elastically deformed and the chuck claw members press the radially outer surface (Wa) of the workpiece from the radially outer side. leaf spring members arranged at a predetermined pitch along a circumferential direction of the chuck structure so as to be symmetrical with respect to a mechanism center axis; chuck claw members mounted to distal ends of the leaf spring members, respectively; and a pressing force applying mechanism configured to apply a force of pressing the leaf spring members radially inward, to thereby elastically press the chuck claw members onto a radially outer surface (Wa) of the workpiece, wherein in a free state, each of the leaf spring members extends straight and is arranged in an oblique posture so that a distal end side of each of the leaf spring members is directed radially outward, wherein the pressing force applying mechanism comprises a pressing member formed of a round bar with a small length, wherein the pressing member is held in contact with a radially outer side of each of the leaf spring members in the free state, in which each of the leaf spring members extends straight, wherein under a state, in which the pressing member is arranged so that an axis thereof is parallel to a direction orthogonal to an axis of the first vertically-movable shaft and an axis of the second vertically-movable shaft, the pressing member is held on a holding frame body mounted to the second vertically-movable shaft, wherein the pressing member is moved up and down with respect to the first vertically-movable shaft, wherein the holding frame body comprises a ring body and a fixed portion fixed to an upper surface of the second vertically-movable shaft with a bolt member, and wherein under a state in which the pressing member is held in contact with the radially outer side of each of the leaf spring members, in response to the ring body raised with respect to the leaf spring members, the pressing member is raised to press a center portion of the leaf spring members in a length direction of the leaf spring members to a distal end boss section side of the first vertically-movable shaft, by which the leaf spring members are pressed radially inward and elastically deformed and the chuck claw members press the radially outer surface (Wa) of the workpiece from the radially outer side.