Disclosed is a rectifying device provided with a standby power reduction function. When a voltage of unsmoothed DC power, which is output from a rectifying unit that rectifies AC power, is lowered to be equal to or smaller than a discharge reference voltage at a time around a zero-crossing point of the AC power, the present invention can instantaneously discharge a capacitor, which has been charged with the unsmoothed DC power, to be synthesized with the unsmoothed DC power, and thus supply stable DC power to a load without using an electrolytic capacitor. In particular, the present invention can adjust a resistance value of a surge prevention switch connected in series with the capacitor to control a current amount flowing through the capacitor, and thus can prevent a surge voltage from being generated when charging and discharging the capacitor.