A method for a coding apparatus comprising: a step of calculating one of frame energy and subframe energy of a speech/sound signal using an auto-correlation operation of the speech/sound signal; and a step of encoding the speech/sound signal using one of the frame energy and the subframe energy, and to generate encoded information, wherein, when performing an auto-correlation operation on the speech/sound signal using equation 1 or equation 2, the calculating step comprises performing auto-correlation operations ∑ i x i-j,x i-m' at a combination of j' and m' for approximation which is different from a combination of j and m in accordance with the values of j and m, and calculating one of the frame energy and the subframe energy by substituting the auto-correlation operations ∑ i x i-j x i-m at the combination of j and m with the auto-correlation operations at the combination of j' and m': E k = ∑ i A i 2 = ∑ j = 0 P − 1 ∑ m = 0 P − 1 α j α m ∑ i x i − j x i − m i = start k, ⋯, end k k = 0, ⋯, N S − 1 E k: energy (subframe energy) of subframe whose subframe index is k, Ai: speech/sound signal after filtering, P: filter order, αj, α m: filter coefficient, xn: (n+1)-th speech/sound signal of subframe, j, m: index indicating delay time when auto-correlation is calculated, i: sample index of speech/sound signal, Ns: number of subframes, k: subframe index, startk: leading sample index of subframe whose subframe index is k, and endk: tail-end sample index of subframe whose subframe index is k; and E = ∑ i A i 2 = ∑ j = 0 P − 1 ∑ m = 0 P − 1 α j α m ∑ i x i − j x i − m i = start, ⋯, end E: frame energy, Ai: speech/sound signal after filtering, P: filter order, αj, αm: filter coefficient, xn: (n+1)-th speech/sound signal of frame, j, m: index indicating delay time when auto-correlation is calculated, i: sample index of speech/sound signal, start: leading sample index of frame, and end: tail-end sample index of frame, and wherein the calculating step further comprises performing control so as to increase the number of combinations of j and m to be substituted with auto-correlation operations at the combination of j' and m' as the difference between j and m in equation 1 or equation 2 increases. a step of calculating one of frame energy and subframe energy of a speech/sound signal using an auto-correlation operation of the speech/sound signal; and a step of encoding the speech/sound signal using one of the frame energy and the subframe energy, and to generate encoded information, wherein, when performing an auto-correlation operation on the speech/sound signal using equation 1 or equation 2, the calculating step comprises performing auto-correlation operations ∑ i x i-j,x i-m' at a combination of j' and m' for approximation which is different from a combination of j and m in accordance with the values of j and m, and calculating one of the frame energy and the subframe energy by substituting the auto-correlation operations ∑ i x i-j x i-m at the combination of j and m with the auto-correlation operations at the combination of j' and m': E k = ∑ i A i 2 = ∑ j = 0 P − 1 ∑ m = 0 P − 1 α j α m ∑ i x i − j x i − m i = start k, ⋯, end k k = 0, ⋯, N S − 1 E k: energy (subframe energy) of subframe whose subframe index is k, Ai: speech/sound signal after filtering, P: filter order, αj, α m: filter coefficient, xn: (n+1)-th speech/sound signal of subframe, j, m: index indicating delay time when auto-correlation is calculated, i: sample index of speech/sound signal, Ns: number of subframes, k: subframe index, startk: leading sample index of subframe whose subframe index is k, and endk: tail-end sample index of subframe whose subframe index is k; and E = ∑ i A i 2 = ∑ j = 0 P − 1 ∑ m = 0 P − 1 α j α m ∑ i x i − j x i − m i = start, ⋯, end E: frame energy, Ai: speech/sound signal after filtering, P: filter order, αj, αm: filter coefficient, xn: (n+1)-th speech/sound signal of frame, j, m: index indicating delay time when auto-correlation is calculated, i: sample index of speech/sound signal, start: leading sample index of frame, and end: tail-end sample index of frame, and E k: energy (subframe energy) of subframe whose subframe index is k, Ai: speech/sound signal after filtering, P: filter order, αj, α m: filter coefficient, xn: (n+1)-th speech/sound signal of subframe, j, m: index indicating delay time when auto-correlation is calculated, i: sample index of speech/sound signal, Ns: number of subframes, k: subframe index, startk: leading sample index of subframe whose subframe index is k, and endk: tail-end sample index of subframe whose subframe index is k; and E: frame energy, Ai: speech/sound signal after filtering, P: filter order, αj, αm: filter coefficient, xn: (n+1)-th speech/sound signal of frame, j, m: index indicating delay time when auto-correlation is calculated, i: sample index of speech/sound signal, start: leading sample index of frame, and end: tail-end sample index of frame, and wherein the calculating step further comprises performing control so as to increase the number of combinations of j and m to be substituted with auto-correlation operations at the combination of j' and m' as the difference between j and m in equation 1 or equation 2 increases.