A voltage converting device includes a feedback module, for generating a comparing signal according to a feedback voltage and a reference voltage; a pulse-width-modulation module, for generating a driving signal according to comparing signal; a voltage-converting module including a low-side switch for controlling a connection between a node and ground according to driving signal, a high-side switch for controlling a connection between the node and an output end according to a control signal, an inductor coupled between the node and an input end, a feedback-voltage-generating unit for generating feedback voltage according to an output voltage of output end and a ratio, an adaptive current-generating unit for generating a current signal according to an adjusting signal, and a control unit for selecting driving signal or current signal as the control signal according to output voltage and an input voltage; and a current-adjusting module for generating adjusting signal according to comparing signal.