A transformer is provided. The transformer includes a first electrical conductor, a second electrical conductor, a circuit board and a core set. The first electrical conductor has a through hole and the second electrical conductor is electromagnetically coupled with the first electrical conductor and includes a plurality of spiral coils formed by winding a single conductive wire, each spiral coil having a through hole. The circuit board has a through hole. The core set penetrates the through hole of the first electrical conductor, the through hole of the circuit board, and the through holes of the plurality of spiral coils of the second electrical conductor, and covers at least one portion of the first electrical conductor and the second electrical conductor.