In an apparatus for recognizing a security code having an electromagnetic band gap (EBG) pattern which uses reflection and transmission characteristics of the EBG pattern, a voltage controlled oscillator generates a signal to a power divider, which divides the power of the signal into halves, and outputs a first signal through a waveguide to be incident on the EBG pattern. The waveguide receives a signal reflected from the EBG pattern and outputs the reflected signal to a phase detector. A circulator outputs the second signal to the phase detector, which detects the phase difference between the reflected signal and the second signal, and outputs phase difference data to a data control unit, which determines whether the security code having the EBG pattern is recognized using the phase difference data. In an alternate embodiment, the voltage control oscillator is controlled to sequentially generate signals using power difference data.