A heating chamber is divided into a plurality of spaces by barrier sections including a conductive material. Phase shifters having different lengths with respect to a direction and including a dielectric body having permittivity higher than air are inserted in positions of a terminal section, in the spaces except for at least one space, to differentiate positions of bottoms of standing microwaves formed in the respective spaces from each other with respect to the direction. In addition, impedance adjusters having different lengths with respect to the direction and including a dielectric body having permittivity higher than air are inserted in positions on an upstream side of a region passed by the object to be heated, in the spaces except for at least one space, to reduce differences in impedance of the spaces from an entrance of the heating chamber to the terminal section including the phase shifters.