Provided is a balanced/unbalanced converter (1) that includes a first strip line (40), a second strip line (41), a third strip line (42), a fourth strip line (43), an unbalanced terminal (4), and an open terminal (7). The first strip line (40) includes a spiral first conductor (19), and the second strip line (41) includes a spiral second conductor (14). An outer circumferential end (19b) of the first conductor (19) is electrically connected to the unbalanced terminal (4), and an outer circumferential end (14a) of the second conductor (14) is electrically connected to the open terminal (7).