Microwave treatment apparatus

A microwave oven includes a waveguide having an E-bend structure with multiple openings disposed on a lateral face of a heating chamber that allow the waveguide to communicate with the heating chamber. The waveguide has a first section for propagating a microwave from a magnetron toward the heating chamber, and a second section having a wide plane that abuts an outer wall of the heating chamber. The openings include at least one circularly-polarized-wave opening for generating a circularly polarized wave. A cross section of the first section orthogonally intersects a tube axis of the first section projects virtually along the tube axis of first section and onto a lateral face of the heating chamber, and the circularly-polarized-wave opening is configured such that its center is located outside the resultant projected region.