A power divider/combiner includes a first transmission line that includes a first part and a second part, and a second transmission line and a third transmission line that are electromagnetically coupled with the first transmission line. The first part, the second part, the second transmission line and the third transmission line are each of a particular length. The first part, the second transmission line and the third transmission line are respectively connected to a first port, a second port and a third port for inputting/outputting signals having a target wavelength equal to four times the particular length.