The present disclosure enhances flexibility, enables the transmission of power, and improves reliability using a simple, low-cost, easy-to-manufacture configuration by disposing a pair of power supplying lines on the outside in the longitudinal direction of the rectangular cross-section of a dielectric. Here, a waveguide is provided with a solid dielectric, a pair of power supplying lines and an external conductor surrounding the dielectric. The solid dielectric has a rectangular cross-section. The pair of power supplying lines are disposed on the outside in the longitudinal direction of the cross-section of the dielectric. The outer surface of the dielectric is slidably in close contact with the inner surface of the external conductor.