The present invention relates to a hog ring clamping device such as a C ring clamping device. In the hog ring clamping device of the invention, a hog ring magazine and jaws are provided to a hog ring clamping device body. A main pneumatic cylinder for moving the jaws pivotally is installed. A feed pneumatic cylinder is attached to the hog ring clamping device body. At least one feed member is mounted to a piston rod of the feed pneumatic cylinder with a unidirectional rotating device therebetween. The feed member is placed in a position for contact with hog rings engaged with the hog ring magazine. A bracket is mounted on the hog ring clamping device body. An arm is mounted pivotally to the bracket and a unidirectional rotating device is mounted to the arm. A presser wheel is mounted on the unidirectional rotating device, and a rod is attached to the arm. A coil spring is used to connect the arm with the bracket resiliently. One end of a flat spring is held between the feed pneumatic cylinder and a bracket for mounting the feed pneumatic cylinder to the hog ring clamping device body. Another end of the flat spring is fixed to the arm, and an extrusion portion extruding toward the neighborhood of the feed member is provided on the flat spring.