A signal transmission line includes a laminate, a signal conductor, a hollow portion, and a reinforcing conductor. The laminate includes a flexible laminate including resin layers each of which has flexibility. The signal conductor extends in a signal transmission direction of the laminate and is disposed in an intermediate position in a laminating direction of the resin layers. The hollow portion is in the laminate and defined by an opening provided at a portion of the plurality of resin layers. The reinforcing conductor is in the laminate. The hollow portion is disposed at a position overlapping with the signal conductor, in a plan view of the laminate from a surface perpendicular or substantially perpendicular to the laminating direction. The reinforcing conductor is disposed at a position different from the position of the hollow portion in a plan view.