A signal line installation structure of an elongated member includes a signal line that is installed between an inner circumferential surface of an outer skin tube and outer circumferential portions of a rigid portion and a flexible portion, where the signal line is installed according to an installation structure according to which the signal line includes a spiral portion that is helically wound around the rigid portion and the flexible portion with an electrical connection portion on the outer circumference of the rigid portion as a winding start point. The spiral portion may prevent disconnection by reducing the bending stress of tension and compression that is applied to the signal line itself when the flexible portion is bent.
