Abstract: A method for controlling a welding current in a resistance welder which phase-controls an A.C. power supply voltage by a thyristor to control the welding current to a target value. Prior to supplying the welding current, a test current is supplied to measure a power-factor angle of a load. A plurality of curves representing relations between the welding currents and control voltages to a phase-shift pulse generator for a plurality of power-factor angles of the load are presets and one of the curves is selected in accordance with the selected power-factor angle of the load. A variation of the A.C. power supply voltage is measured. A period of a pulse generated by the phase-shift pulse generator is controlled based on a value determined in accordance with the selected curve and the measured variation of the A.C. power supply voltage to control a firing angle of the thyristor.