The present invention discloses a production method of a foamed electric wire, whereby a foamed electric wire is obtained via a foamed insulation layer formation step of forming a foamed insulation layer on a conductor, wherein the foamed insulation layer formation step includes: a step of introducing a base resin into an extruding machine, a step of introducing a foaming agent into the extruding machine, and a step of extruding a mixture containing the base resin and the foaming agent from the extruding machine and forming the foamed insulation layer on the conductor, and wherein the resin contained in the mixture has a shear stress of 0.40 to 0.80 Mpa, and the base resin is a propylene-based resin.