A clamping apparatus comprising: a housing; a locking member protruding toward a leading end side relative to the housing and configured to be insertable into a hole (Wa) of a to-be-clamped object; a clamp rod including a wedge surface configured to be engaged with the locking member from the leading end side; a driving means configured to drive the clamp rod toward a base end side for clamping action and to drive the clamp rod toward the leading end side for unclamping action; a support member supporting a base end portion of the locking member so that the locking member is radially movable, the support member being inserted in a leading-end-side portion of the housing so as to be movable in its axial direction; a resistance giving mechanism configured to give resistance to axial movement of the support member; and an engagement maintaining mechanism which allows the wedge surface of the clamp rod to be engaged with the locking member so as to be movable relative to each other, wherein the support member includes a tubular portion in which the clamp rod is inserted so as to be movable in the axial direction, characterised in that the resistance giving mechanism includes: an annular groove provided on an outer peripheral surface of the tubular portion; and a ring-like elastic member attached to the annular groove, wherein an annular groove is provided on an inner peripheral surface of a tubular upper housing, and the elastic member is fitted in the groove in an unclamping state, and wherein when the clamp rod is driven toward the leading end side for unclamping action, the clamp rod moves the locking member toward the leading end side via the support member after the locking member moves radially inward. a housing; a locking member protruding toward a leading end side relative to the housing and configured to be insertable into a hole (Wa) of a to-be-clamped object; a clamp rod including a wedge surface configured to be engaged with the locking member from the leading end side; a driving means configured to drive the clamp rod toward a base end side for clamping action and to drive the clamp rod toward the leading end side for unclamping action; a support member supporting a base end portion of the locking member so that the locking member is radially movable, the support member being inserted in a leading-end-side portion of the housing so as to be movable in its axial direction; a resistance giving mechanism configured to give resistance to axial movement of the support member; and an engagement maintaining mechanism which allows the wedge surface of the clamp rod to be engaged with the locking member so as to be movable relative to each other, wherein the support member includes a tubular portion in which the clamp rod is inserted so as to be movable in the axial direction, characterised in that the resistance giving mechanism includes: an annular groove provided on an outer peripheral surface of the tubular portion; and a ring-like elastic member attached to the annular groove, wherein an annular groove is provided on an inner peripheral surface of a tubular upper housing, and the elastic member is fitted in the groove in an unclamping state, and wherein when the clamp rod is driven toward the leading end side for unclamping action, the clamp rod moves the locking member toward the leading end side via the support member after the locking member moves radially inward. an annular groove provided on an outer peripheral surface of the tubular portion; and a ring-like elastic member attached to the annular groove, wherein an annular groove is provided on an inner peripheral surface of a tubular upper housing, and the elastic member is fitted in the groove in an unclamping state, and wherein when the clamp rod is driven toward the leading end side for unclamping action, the clamp rod moves the locking member toward the leading end side via the support member after the locking member moves radially inward.