PURPOSE: To easily attach and detach an electrode with a simple clamp system in a device to attach an electrode ring at the top end of an electrode shaft.

CONSTITUTION: In a device to tighten an electrode ring 2 to the top end of an electrode shaft l in a seam welding machine, the device has a shaft 4 inserted on the central axis (A-A) of the electrode shaft, and a acting means 3 with a hydraulic pressure or an elastic force connected to this shaft, and this acting means 3 generates an energizing force to the direction drawing-in the electrode ring held at the shaft top, or releases the energizing force. Up to now, in a case of attaching the electrode ring to the electrode shaft, fixing is executed by tightening a bolt, however in a case of using this device, because it is the clamp system, a bolt tightening or a detaching trouble is eliminated, tightening is made simple, the maintaining working is shortened and the automation can be also embodied.