To provide an extension joint for an electric wire capable of preventing position deviation of a conductive body of each joint part of a plurality of electric wires and improving a fusion joining quality of each conductive body.

In an extension joint method of electric wires in which an insulation covered part 2a of each joint part of plural wires 1 is peeled and conductive bodies of each exposed joint part J are fused/joined each other between a pair of electrodes, fusion joining of conductive bodies of plural electric wires is conducted each other dividing in plural times. That is, the conductive body 2b of each joint part J of remaining electric wires 2 is successively extended and is fusion-joined one by one to one of the joint parts J among each joint part of the conductive body of the plural electric wires 2.