A DC motor device includes a first converting circuit, a second converting circuit, and a DC motor. A switch element is coupled to the DC motor device, and provides an alternating current to the first or second converting circuit. The first converting circuit receives the alternating current, and generates a first rotation speed signal. The second converting circuit receives the alternating current, and generates a second rotation speed signal. The DC motor is driven at a rotation speed according to the first or second rotation speed signal.