A Balun circuit manufactured by integrate passive device (IPD) process. The Balun circuit includes a substrate, a first coplanar spiral structure, and a second coplanar spiral structure. One end of the innermost first left coil of the first coplanar spiral structure is electrically connected to the innermost first right coil through a first bridge. Two ends of the first coplanar spiral structure are electrically connected to the outermost first left coil and the outermost right coil respectively. One end of the innermost second left coil of the second coplanar spiral structure is electrically connected to the innermost second right coil through a second bridge. Two ends of the second coplanar spiral structure are electrically connected to the outermost second left coil and the outermost second right coil respectively. The first left coils and the second left coils are interlaced. The first right coils and the second right coils are interlaced.