PURPOSE: To eliminate a time delay of pressure and electric conduction by placing an electrode on one end of members connected to each other so as to be rotatable, providing a pressurizing means operated by a pneumatic pressure on the other end, and providing a control means which can execute the electric conduction, on the pressurizing means.

CONSTITUTION: When object to be welded 36, 38 are placed between electrode fingers 22, 26 and a cover 68 is pushed by the inside of the thumb, air of a passage 40 is transmitted to a passage 48 by movement of a valve shaft 62 and a pneumatic pressure in a chamber 50 rises, and a piston 72 is pushed to the outside from a cylinder 70. At the same, members 16, 18 connected to the piston 72 and the cylinder 70 are turned around a pivot 20, the fingers 22, 26 clamp strongly the objects to be welded 36, 38, and also, when the pressure in the chamber 50 rises enough, a welding circuit is formed by the piston 72. In this way, when clamping the object to be welded, a time delay of a pressure and an electric conduction of the finger is eliminated, and welding can be executed exactly.