To easily form a bead shape with a desired dilution ratio in build-up welding method for an inconel by AC pulse arc welding.

Regarding the build-up welding method for an inconel by AC pulse arc welding where an electrode minus polarity current is made to flow in an electrode minus polarity period, a peak current and a base current are made to flow in an electrode plus polarity period, and the electrode minus polarity period is adjusted, thus an electrode minus polarity current ratio is made proper, so as perform welding, a dilution ratio set value Rk is beforehand set, with the dilution ratio set value Rk as an input, the electrode minus polarity period Tnr is calculated by beforehand decided period set functions TNR, the electrode minus polarity current ratio is made proper by the calculated electrode minus polarity period Tnr, and a bead shape with a dilution ratio set by the dilution ratio set value Rk is formed.