A signal processing apparatus comprising: a demultiplexing unit that demultiplexes input encoded data into low band encoded data and high band encoded data; a low band decoding unit that decodes the low band encoded data to produce a low band signal; a high band decoding unit that decodes the high band encoded data to obtain a fixed length index, a switching flag, and a coefficient index that indicates a decoded high band sub-band power estimation coefficient, and supplies the decoded high band sub-band power estimation coefficient, the fixed length index, and the switching flag to a selection unit; a high band sub-band power calculation unit comprising the selection unit, wherein the selection unit selects a decoded high band sub-band power estimation coefficient of a frame to be processed from the decoded high band sub-band power estimation coefficient supplied from the high band decoding unit based on the fixed length index and the switching flag supplied from the high band decoding unit, wherein the high band sub-band power calculation unit calculates a high band sub-band power of a high band sub-band signal of each sub-band constituting the high band signal of the frame to be processed based on a low band sub-band power of a low band sub-band signal of a plurality of sub-bands constituting the low band signal of the frame to be processed and the selected decoded high band sub-band power estimation coefficient; and a high band signal production unit that produces the high band signal of the frame to be processed based on the high band sub-band power and the low band sub-band signal; wherein the fixed length index obtained by the high band decoding unit indicates a fixed length of a fixed length segment of the high band encoded data and the switching flag obtained by the high band decoding unit indicates whether the coefficient index of the fixed length segment is changed at a boundary position between the fixed length segment and a next fixed length segment of the high band encoded data, and wherein when the switching flag indicates that the coefficient index is the same, the high band encoded data does not include the coefficient index of the next fixed length segment, and when the switching flag indicates that the coefficient index is not the same, the high band encoded data further includes the coefficient index of the next fixed length segment. a demultiplexing unit that demultiplexes input encoded data into low band encoded data and high band encoded data; a low band decoding unit that decodes the low band encoded data to produce a low band signal; a high band decoding unit that decodes the high band encoded data to obtain a fixed length index, a switching flag, and a coefficient index that indicates a decoded high band sub-band power estimation coefficient, and supplies the decoded high band sub-band power estimation coefficient, the fixed length index, and the switching flag to a selection unit; a high band sub-band power calculation unit comprising the selection unit, wherein the selection unit selects a decoded high band sub-band power estimation coefficient of a frame to be processed from the decoded high band sub-band power estimation coefficient supplied from the high band decoding unit based on the fixed length index and the switching flag supplied from the high band decoding unit, wherein the high band sub-band power calculation unit calculates a high band sub-band power of a high band sub-band signal of each sub-band constituting the high band signal of the frame to be processed based on a low band sub-band power of a low band sub-band signal of a plurality of sub-bands constituting the low band signal of the frame to be processed and the selected decoded high band sub-band power estimation coefficient; and a high band signal production unit that produces the high band signal of the frame to be processed based on the high band sub-band power and the low band sub-band signal; wherein the fixed length index obtained by the high band decoding unit indicates a fixed length of a fixed length segment of the high band encoded data and the switching flag obtained by the high band decoding unit indicates whether the coefficient index of the fixed length segment is changed at a boundary position between the fixed length segment and a next fixed length segment of the high band encoded data, and wherein when the switching flag indicates that the coefficient index is the same, the high band encoded data does not include the coefficient index of the next fixed length segment, and when the switching flag indicates that the coefficient index is not the same, the high band encoded data further includes the coefficient index of the next fixed length segment.