Provided is a signal encoding apparatus including: an encoding unit which encodes a quantization value of a frequency spectrum in an input signal through a plurality of encoding algorithms; an amplitude change amount calculation unit which calculates an amplitude change amount with respect to the frequency spectrum based on a spectrum envelope of the frequency spectrum; and an encoding selection unit which selects the encoding algorithm according to a degree of deflection of an occurrence probability distribution of the quantization value in the amplitude change amount among the plurality of the encoding algorithms.