A duct includes: a tube that is formed to extend from an indoor of a building or a movable body and that allows an outside and the indoor to communicate with each other; an electromagnetic wave inhibiting sloped surface that is formed on an inner surface of the tube and extends to be sloped to approach an axial line of the tube from the outside toward the indoor in an axial direction of the tube and that reflects an electromagnetic wave; and an electromagnetic wave selecting inner peripheral member that has a tubular shape covering the electromagnetic wave inhibiting sloped surface from an inner peripheral side and is capable of selectively transmitting only an electromagnetic wave of a specific frequency incident on the tube.