To provide an induction heating apparatus that can change an electromagnetic wave of linearly polarized light to an electromagnetic wave of a circularly polarized light with a waveguide disposed at a path to a heating chamber from a magnetron and transfer the electromagnetic wave of circularly polarized light to the heating chamber.

A magnetron 28 sends an electromagnetic wave of linearly polarized light into a waveguide 32 through an antenna 30 passing through an inlet opening 34 formed on a sidewall of the waveguide 32. A pair of plate- like conversion formations 35 are provided in the waveguide 32, and an electromagnetic wave of a linearly polarized light is changed to an electromagnetic wave of a circularly polarized light by the conversion formations 35, and is introduced into the heating chamber 34 from the opening end of the waveguide 32.