In an impedance conversion circuit, a first coil element and a third coil element are arranged coaxially adjacent to each other, and a second coil element and a fourth coil element are arranged coaxially adjacent to each other. By arranging the first and third coil elements in close proximity and arranging the second coil element and the fourth coil element in close proximity in a layering direction, the first coil element is mainly magnetically coupled with the third coil element, and the second coil element is mainly magnetically coupling with the fourth coil element. The first coil element is connected in parallel to the second coil element, and the third coil element is connected in series to the fourth coil element.