The present invention relates to an apparatus for blocking standby power of computer peripheral devices, comprising: a synchronization signal sensing control unit which senses the existence of horizontal and vertical synchronization signals provided to a monitor from a computer body, and outputs a switching control signal according to the sensed result; and a power switching unit which is provided with external power and situated on a power supply path for supplying power to the computer peripheral devices, and has a structure adapted for conducting or blocking the corresponding path according to the switching control signal.