A balanced-unbalanced converting circuit includes first to fourth strip lines of a quarter wavelength or less. The first strip line has an end connected with a balanced terminal, and the third strip line has an end connected with an unbalanced terminal. The end of the first strip line connected to the balanced terminal opposes the end of the third strip line connected to the unbalanced terminal so that the first and third strip lines are electromagnetically coupled so as to define a coupler. The second strip line has an end connected with a balanced terminal, and the fourth strip line has an end connected with an open terminal. The end of the second strip line connected to the balanced terminal opposes the end of the fourth strip line connected to the open terminal so that the second and fourth strip lines are electromagnetically coupled so as to define a coupler.
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