To provide an extension method for transmission line and a metal wheel for extension therefor capable of preventing excessive deformation from being received while a transmission line of which cross section is oval is being passed through the metal wheel.

This extension method is a method of extending the transmission line 5 having an oval cross section, of which long-diameter part B is spirally disposed in the lengthwise direction by twisting, by passing it through the metal wheel 1 mounted on a steel tower 6. A recessed and protruding section 4 meeting the cross-section shape of the transmission line 5 changing at prescribed pitches in the lengthwise direction is formed on the circumference of a wheel body 3 of the metal wheel 1.