Provided is a spectrum estimation apparatus which comprises: a threshold setting unit to set one or more threshold values so as to divide a spectrum in more than one energy bins; a reference value setting unit to set one of a plurality threshold values as a threshold value; a threshold adjustment unit to adjust the plurality of threshold values so as to correspond to the predetermined purpose; a comparison unit to compare the reference threshold value and the adjusted threshold value; and an output unit which the adjusted threshold value outputs the determined spectrum in case that as a result of the comparison, the comparison value corresponds to the predetermined maximum value. [Reference numerals] (110) Threshold setting unit; (120) Reference value setting unit; (130) Threshold adjustment unit; (140) Comparison unit; (150) Output unit
