Provided is an apparatus for spectrum estimation. The apparatus includes a threshold setter which sets at least one threshold in order to separate a spectrum into at least one energy bin; a reference value setter which sets one of the at least one threshold as a reference threshold; a threshold adjuster which adjusts the at least one threshold based on a predetermined condition; a comparer which compares the reference threshold with the adjusted threshold; and an output unit which outputs a spectrum in which the adjusted threshold is set, when a value which is determined based on the comparison result corresponds to a predetermined maximum value.