To weld a lead wire even in a case of displacing the position of a welding pad on an electric circuit substrate by composing electrodes for welding the parallel gap in a shape of surrounding the main electrode with two sub electrodes.

An electric circuit substrate 5 is supplied under a welding equipment. A main electrode 1 and sub electrodes 2 are lowered. The sub electrodes 2 are made in contact with a welding pad 7 of an object to be welded on the electric circuit substrate 5. The main electrode 1 is made in contact with a lead wire 7 on the welding pad 7. The voltage is applied between the electrodes 1, 2, and the lead wire 6 is welded to the pad 7. After welding, the main electrode 1 and the sub electrodes 2 are raised and the electric circuit substrate 5 is discharged from the welding equipment. The allowable positional tolerance d=c/2 is larger than the allowable positional tolerance d=c/2-(a+2b)/4 of the welding equipment of the conventional one sub electrode 2. Even if the welding pad 7' is displaced in the position, when the welding pad is lain under the lead wire 6, those are welded surely.