To efficiently perform pressure welding by preventing a gap from being generated even if rails are is subtly twisted.

The welding machine is equipped with pads 39, 40 which come in contact with both sides of rails and a chuck body 38 which holds the pads 39, 40 so as to make them freely oscillatable in such a manner that the pads 39, 40 oscillate at least in accordance with the twist of the rails to bring the operating face of the pads in face contact with both sides of the rails. Thus, even if the rails are subtly twisted, the pads 39, 40 prevent a gap from being generated between the pad and the side of the rails by oscillating in accordance with the twist.