A signal line installation structure of an elongated member includes a signal line 6 that is installed between an inner circumferential surface of an outer skin tube 2 and outer circumferential portions of a rigid portion 4 and a flexible portion 5, where the signal line 6 is installed according to an installation structure according to which the signal line 6 includes a spiral portion 6b that is helically wound around the rigid portion 4 and the flexible portion 5 with an electrical connection portion 6a on the outer circumference of the rigid portion 4 as a winding start point. The spiral portion 6b may prevent disconnection by reducing the bending stress of tension and compression that is applied to the signal line 6 itself when the flexible portion 5 is bent.
