A clamping device having a high clamping force and operability when a cutting insert is attached/detached is provided. The clamping device has a guide hole, a screw hole, a clamp member having a clamp portion and arranged movably in the guide hole, and a screw member screwed with the screw hole and movable in first and second directions, wherein the screw member can be engaged with the clamp member in movement both in the directions and the guide hole has a first cam surface engaged with the clamp member and converting a force in the first direction received from the screw member into a force for moving the clamp member in a direction toward the cutting insert and a second cam surface converting a force in the second direction into a force for moving the clamp portion in a direction away from the cutting insert.