A buck voltage converting apparatus is disclosed. The buck voltage converting apparatus includes a first transistor, a second transistor, an inductor, a controller and a switch. The first transistor receives an input voltage. A first terminal of the inductor is coupled to the first and second transistors. A second terminal of the inductor is coupled to an output terminal of the buck voltage converting apparatus for generating an output voltage. The controller receives the output voltage, and generates a detection voltage according to voltage amplitude of the output voltage. The switch is coupled between a first terminal of the first transistor and a control terminal of the second transistor. The switch is turned on or off according to the detection voltage.