A voltage regulating device and a mode switching detecting circuit are provided. The mode switching detecting circuit is configured to reset a soft start circuit of the voltage regulating device. The mode switching detecting circuit includes a mode switching signal detector, a reset signal generator, and a reset status detector. The mode switching signal detector receives a mode switching signal and generates a setting signal according to a transition edge of the mode switching signal. The reset signal generator is coupled to the mode switching signal detector and generates a reset activating signal according to the setting signal. The reset activating signal drives the soft start circuit to perform a reset operation. The reset status detector compares an output voltage of the soft start circuit and a reference voltage to generate a clear signal. The reset signal generator clears the reset activating signal according to the clear signal.