A left-handed ferrite waveguide with antiparallel bias magnetic field is investigated. Nonreciprocal dispersion diagram, scattering parameters, and field profiles are numerically calculated, and seamless transition from the RH to LH mode with energy transmission is shown as well as conventional seamless transition from the LH to RH mode. It has possibility of application to the nonreciprocal phase shifter and gyrator which have magnetic tunability.