An AC TIG welding apparatus using a hot wire is disclosed. An unconsumable electrode (5) such as of tungsten is arranged in opposedly spaced relationship with a base metal (6) to be welded. An AC arc welding power supply (2) is connected between the base metal (6) and the unconsumable electrode (5). A filler wire (9) such as of aluminum is fed toward an arc-generated part between the base metal (6) and the unconsumable electrode (5). A wire feeder (8) supplies the filler wire (9). An unconsumable-­electrode welding apparatus comprising the above-mentioned devices further comprises a wire-heating power supply (3) for producing a pulsed current. The wire heating power supply (3) heats the filler wire (9) by supplying thereto a pulsed current in accordance with a synchronous signal from the AC arc welding power supply (2) or a detection signal of an arc current i A or an arc voltage of the AC arc power supply (2).The filler wire (9) is thus heated by being supplied with a heating current i W in pulse form while the unconsumable electrode (5) is kept negative by an AC arc (7) formed between the unconsumable electrode (5) and the base metal (6). During the period when the unconsum­able electrode (5) is kept positive by the AC arc (7), on the other hand, the filler wire (9) is not supplied with any current or is heated by being supplied only with a sufficiently small current not to cause any substantial magnetic flow. Accordingly, even if a large current flows through the wire (9), arc interruptions can be eliminated, thereby improving the welding process of aluminum by using an AC TIG arc.