A directional input device with a light directing shaft that avoids wear and tear caused by physical contact between a shaft and a sensor surface. At least one of the wire feeding units includes a torque limiter provided in a driving transmission system thereof for transmitting a driving force from a driving source to the welding wire. has high refractivity, low dispersiveness, heat resistance, good transparency and good releasability from mold. In another embodiment, the two-position valve employs sized leak paths so that when the two-position valve is in the closed position, the cathode exhaust gas can still flow through. A control device moves the control valve to close the leak passage when activated and makes it ineffective when deactivated so that the pressure chamber communicates with the fluid-reservoir chamber via the leak passage.