This paper has proposed a method constructing composite right/left-handed cylindrical waveguides. In this waveguide, negative permeability is realized by the cut-off TM01 mode in a hollow waveguide and also negative permittivity is realized by the cutoff dominant TE mode in a sector waveguide with a ridge. Usefulness of the proposed cylindrical waveguide is verified from the calculated values for the transmission characteristics of the structure with the finite-number unit cells. Also effectiveness of composite right/left-handed leaky-wave antenna is verified from forward and backward radiation characteristics numerically.