PROBLEM TO BE SOLVED: To provide a one-side resistance spot welding method and one-side resistance spot welding equipment which provide uniform and stable welding quality.SOLUTION: The one-side resistance spot welding equipment includes: a welding electrode 16 that abuts on a weld part 50a of members 50 to be welded in which a first plate member 51 and a second plate member 52 are superimposed, and that applies pressure to the member 51 to be welded; a sub-electrode 26 which is annularly shaped surrounding the welding electrode 16 coaxially with it and which abuts on the member to be welded at the distal end 26a; a grounding electrode 30 that is in contact with the second plate member 52; and a welding energization circuit 40 which makes a welding current flow between the welding electrode 16 and the grounding electrode 30 and which makes a sub-electric current flow between the sub-electrode 26 and the grounding electrode 30. The sub-electric current i flowing from the distal end 26a of the sub-electrode 26 to the first plate member 51 raises the potential of a part surrounding the weld part 50a, suppresses an ineffective branching current flowing in the first plate member 51 from the welding electrode 16, the welding current is made to flow concentratedly on a welding energization route X, and a nugget N is efficiently formed in the junction (a).
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