When an operation portion (38) provided at an axial end portion of a valve member (37) is pushed into a valve case (31) provided to a first block (3), a clamping apparatus transitions from a first state, in which communication between: each of a primary-side pressure fluid supply/discharge port (34) and a secondary-side pressure fluid supply/discharge port (35); and a pressure fluid discharge port (36) is open, to a second state, in which communication between: each of the primary-side pressure fluid supply/discharge port (34) and the secondary-side pressure fluid supply/discharge port (35); and the pressure fluid discharge port (36) is closed.