Provided are a device and method for detecting a wiretapping device using a power line and nullifying the wiretapping device. More particularly, a device and method for preventing wiretapping, which sense a wiretapping signal from a power line and transmit a noise signal to the power line, are provided. The device for preventing wiretapping includes: a signal detector for receiving signals from a power line and filtering the received signals in at least one frequency band; a controller for receiving the filtered signal from the signal detector and determining whether a wiretapping signal exists; and a noise signal output unit for transmitting a noise signal to the power line according to whether or not the wiretapping signal exists. The device can detect wiretapping and simultaneously nullify the function of the wiretapping device by detecting a wiretapping signal from a power line and transmitting a noise signal having a frequency corresponding to a frequency band of the wiretapping signal.