PURPOSE: To extend the service life of a concrete structure and to improve safety of work by providing a hollow guide surrounding reinforcing bars or wires and introducing inert gas into the guide as necessary to perform electric pressure welding on the reinforcing bar or wire.

CONSTITUTION: The hollow guide 27 is set between electrodes 25 and 26 and the end faces of the reinforcing bars or wires 29 and 30 are fitted at the hollow part 28 and pressed and electrified. A part 33 where a bulge of a clad part is formed is pressed against a hollow part inner wall 34 and the occurrence of the bulge of the molten clad part is prevented. Further, as necessary, the inert gas is introduced into the guide 27 to perform pressure welding. By this method, since the performance as the concrete reinforcing bars is displayed fully, the service life of the concrete structure is extended. Further, since the scatter of a spark at the time of pressure welding is prevented, the safety of the work is also improved.