A transformer device includes a first and a second trace, a first and a second connection member, and a first input/output member. A second sub-trace of the first trace is coupled to a first sub-trace of the first trace at a first and a second area. The first connection member is coupled to the first and the second sub-trace. The first and a third sub-trace of the second trace are disposed in turn. A fourth sub-trace of the second trace is coupled to the third sub-trace at the first and the second area. The second and the fourth sub-trace are disposed in turn. The second connection member is coupled to the third and the fourth sub-trace. The first sub-trace includes first wires, and the first input/output member is coupled to the first wire which is located at an inner side among the first wires.