A clamp changing apparatus includes a coupling device capable of being secured on a robot arm and a clamp-holding device. The coupling device includes a main body defining a blind hole, a connecting portion defining a through hole communicating with the blind hole, and a piston. The connecting portion has a ring-shaped protrusion aligned with the through hole facing away from the main body. The protrusion defines a plurality of holes running through the lateral wall thereof, each of the holes receives a rigid ball in which the diameter is bigger than the depth of the hole. The piston is received in the blind hole and the through hole, and is slidable along them to push the rigid balls out of the protrusion. The clamp-holding device is capable of being fixed to a clamp and defines a latching hole corresponding to the protrusion.