A three-way power divider (51, 52), comprising: a rectangular waveguide having a waveguide wall, the waveguide wall being formed by a first L-shaped waveguide, a first flat waveguide, a second L-shaped waveguide, a third L-shaped waveguide, a second flat waveguide (le), and a fourth L-shaped waveguide arranged in a ring shape; an input waveguide having one end connected between the first L-shaped waveguide (la) and the fourth L-shaped waveguide and another end connected to a first port (2, 3, 4, 5); a first output waveguide having one end connected between the first L-shaped waveguide (la) and the first flat waveguide and another end connected to a second port (2, 3, 4, 5); a second output waveguide having one end connected between the first flat waveguide and the second L-shaped waveguide and another end connected to a third port (2, 3, 4, 5); a third output waveguide having one end connected between the second L-shaped waveguide and the third L-shaped waveguide, or between the second flat waveguide and the fourth L-shaped waveguide and another end connected to a fourth port (2, 3, 4, 5); and a plurality of branching waveguides each having one end connected to the first output waveguide and another end connected to the second output waveguide., wherein a difference between a sum of electrical lengths of the second L-shaped waveguide, the third L-shaped waveguide, the second flat waveguide (le), and the fourth L-shaped waveguide and a sum of electrical lengths of the first L-shaped waveguide (la) and the first flat waveguide is a multiple of a half of a wavelength of a propagating signal by a factor of N, N being an odd number, at a frequency of a fundamental wave of the propagating signal. a rectangular waveguide having a waveguide wall, the waveguide wall being formed by a first L-shaped waveguide, a first flat waveguide, a second L-shaped waveguide, a third L-shaped waveguide, a second flat waveguide (le), and a fourth L-shaped waveguide arranged in a ring shape; an input waveguide having one end connected between the first L-shaped waveguide (la) and the fourth L-shaped waveguide and another end connected to a first port (2, 3, 4, 5); a first output waveguide having one end connected between the first L-shaped waveguide (la) and the first flat waveguide and another end connected to a second port (2, 3, 4, 5); a second output waveguide having one end connected between the first flat waveguide and the second L-shaped waveguide and another end connected to a third port (2, 3, 4, 5); a third output waveguide having one end connected between the second L-shaped waveguide and the third L-shaped waveguide, or between the second flat waveguide and the fourth L-shaped waveguide and another end connected to a fourth port (2, 3, 4, 5); and a plurality of branching waveguides each having one end connected to the first output waveguide and another end connected to the second output waveguide., wherein a difference between a sum of electrical lengths of the second L-shaped waveguide, the third L-shaped waveguide, the second flat waveguide (le), and the fourth L-shaped waveguide and a sum of electrical lengths of the first L-shaped waveguide (la) and the first flat waveguide is a multiple of a half of a wavelength of a propagating signal by a factor of N, N being an odd number, at a frequency of a fundamental wave of the propagating signal.