An electromagnetic interference prevention apparatus for a flat panel display which is capable of modulating the frequency of an input clock signal using a spread spectrum clocking method to increase the frequency of the clock signal and reduce the amplitude thereof so as to reduce EMI by a clock signal generated from a format converter of the flat panel display. An X-ray detector detects X-rays generated from the X-ray tube and transmitted through an object to be examined. The first all-pass network includes the resonator and the second all-pass network includes a resistor having resistance matched to a motional resistance of the resonator at the resonant frequency.