PURPOSE: To improve the reliability of the welding quality, by connecting an output means, which designates a retrieval address of phase conversion data, to a phase conversion data outputting means and designating the retrieval address of phase conversion data successively in accordance with the growth of a nugget.

CONSTITUTION: In the resistance welding device which controls the welding current in accordance with the growth of a nugget, a table number is designated in a phase conversion data outputting circuit 37 by the table number designating signal from a retrieval address designator 38 just before welding, and phase conversion data of an SCR 17 corresponding to the differential voltage in the table having this compensated number is retrieved. This data is inputted to a phase controlling circuit 11 to adjust successively the firing angle of the SCR 17 through a thyristor, a trigger pulse generating circuit 14, and a switching element 16, and the value of the welding current is increased or reduced in every half cycle. After the generation process for one nugget, the table number designating signal for the next process is outputted from the table number designator 38 to correct the talbe number of the initially set phase conversion data table. This operation is repeated in every generation process of the nugget to advance welding.