ELECTRIC WIRE CONNECTION STRUCTURE AND ELECTRIC WIRE CONNECTION METHOD

A harness 1 is provided with one or more first electric wires 10A provided with a first core wire exposed part 11AE, one or more second electric wires 10B provided with a second core wire exposed part11BE, and a joining part 20 to which the first core wire exposed part 11AE and the second core wire exposed part 11BE are welded. A gross cross-sectional area A2 of second core wires 11B is one thirdor less of the sum (A1+A2) of gross cross-sectional areas of first core wires 11A and the second core wires 11B. The joining part 20 has two pairs of outer surfaces extending along the extension direction of the first electric wire 10A and the second electric wire 10B, and facing each other, a distance H between outer surfaces (upper surface Up, under surface Ud) that form one pair out of the twopairs of outer surfaces is longer than a distance W between outer surfaces (right side surface R, left side surface L) that form the other pair, and in the joining part 20, the second core wire exposed part 11BE is disposed to