A clamping apparatus includes: a support member (19) inserted in a leading-end-side portion of the housing (1) so as to be movable in its axial direction; a resistance giving mechanism (34) configured to give resistance to axial movement of the support member (19); and an engagement maintaining mechanism (26) configured to maintain engagement between a wedge surface (24) of a clamp rod (7) and a locking member (23). When the clamp rod (7) is driven toward a leading end side for unclamping action, the clamp rod (7) moves the locking member (23) toward the leading end side via the support member (19) after the locking member (23) moves radially inward.