A digital door lock system includes a receiving antenna matching unit configured to receive a power signal wirelessly transmitted from the wireless power transmitting device; a full-wave rectifying unit configured to convert a sinusoidal signal waveform outputted from the receiving antenna matching unit to one of constant polarity; a voltage regulating unit configured to stabilize a signal outputted from the full-wave rectifying unit; a secondary battery configured to supply a power in case of power outage; an excessive charging/discharging preventing unit configured to charge the secondary battery by a stabilized power of the voltage regulating unit and having an excessive charging/discharging preventing function; and a power supply unit configured to supply the power of the voltage regulating unit to the respective units of the system and to supply the power of the secondary battery to the respective units of the system in the case of power outage.