Provided is an over-voltage protection device for a resonant wireless power transmission device. The over-voltage protection device includes an amplifier for amplifying a transmission signal, a resonance signal generator for generating a wireless resonance signal according to the transmission signal amplified by the amplifier, a voltage detector for sensing a voltage of the wireless resonance signal generated by the resonance signal generator, and a controller for monitoring the voltage detected by the voltage detector to determine whether the voltage repetitively increases and decreases with periodicity when the voltage is greater than a reference voltage and controlling the amplifier to decrease an output of the transmission device by a value according to a result of the determination.