To provide a waveguide capable of suppressing deterioration of transmission characteristics of a signal wave generated due to a dimensional error while extending a usable frequency band.

A waveguide 1 includes a first waveguide conduit 10, a second waveguide conduit 11 and connection space 15 for connecting an end part of the first waveguide conduit 10 to an end part of the second waveguide conduit 11. The connection space 15 is defined by a plurality of wall surfaces including a first wall surface 15a extended in a direction reverse to a second direction from an end edge 10a of the first waveguide conduit 10 as a base end, a first orthogonal wall surface 15d formed orthogonally to the first wall surface 15a to generate a reflected wave capable of resonating with a signal wave advancing in the second direction, a second wall surface 15b extended in a first direction from an end edge 11a of the second waveguide conduit 11 as a base end, and a second orthogonal wall surface 15c formed orthogonally to the second wall surface 15b to generate a reflected wave capable of resonating with a signal wave advancing in the second direction.