A synchronous buck DC/DC converter to perform an improved switching operation by adjusting a variable resistor is provided. The synchronous buck DC/DC converter includes a switching unit for switching two PWM signals inverted with a dead time and outputting the PWM signals, a smoothing circuit for outputting DC power using a waveform output from the switching unit as an input, a variable resistor connected to the switching unit and adjusting a switching time of the waveform output from the switching unit, and a variable resistor controller for sensing a current from an output terminal of the smoothing circuit and setting the resistance of the variable resistor to a resistance corresponding to the sensed current.