In order to provide a resistance welding device and a resistance welding method whereby a determination can be made regarding join quality during joining of conductors by resistance welding, in order to provide a protrusion shape used in projection welding suitable for determinations about join quality, etc., and in order to improve electrical reliability and mechanical join strength by using the resistance welding device, the resistance welding method, and the protrusion shape for projection welding, when connecting conductors in an electric power steering device: a travel amount measurement unit (1007) is provided in the resistance welding device (1000); the gap between conductors (1004, 1005) to be joined is measured before and after joining; an evaluation is made regarding join quality, on the basis of said gap; and, in order to make securing the gap between the conductors after joining easier, a protrusion (200) comprising a base (210) and a protruding surface (230) is provided in the conductor (1005) to be connected.