In an electric power clamping apparatus that locks a clamping arm when it is not driven by an electric motor attached with the a brake mechanism, manual operation of the clamping arm is facilitated. In an electric power clamping apparatus for transmitting an output of an electric motor via a reduction drive system to a clamping arm, an operation shaft including a small gear meshing with a gear that forms a part of the reduction drive system by pressing with an external tool is fit by insertion rotatably and movably back and forth into a body, and a linkage mechanism is provided in the operation shaft for operating a release lever in a brake mechanism to make the brake mechanism inoperative when the small gear meshes with the gear of the reduction drive system.