An apparatus and a method for detecting the energy of a tone signal. A pre-process unit takes absolute values of transmitted samples and outputs the values to a delay unit for delaying the transmitted samples according to a predetermined delay interval. An operation unit subtracts the value calculated by multiplying the magnitudes of the samples transmitted before and after the burst detection from the square value of the magnitude of the sample at the time of burst detection among the delayed transmitted samples. A detection unit detects the burst by confirming whether peaks corresponding to the number of the samples transmitted before the sample of the burst detection are detected by a signal of an value input from the operation unit. Therefore, the present invention can reduce a probability of a false alarm caused by an impulse error and burst errors and thus perform stable burst detection.