An audio encoding device for encoding an audio signal consisting of a plurality of frames, the audio encoding device comprising: an audio encoding unit for encoding an audio encoding target frame of the plurality of frames of the audio signal; and an auxiliary information encoding unit for estimating and encoding auxiliary information about a temporal change of power of the audio signal, the auxiliary information being used in packet loss concealment in decoding of the audio signal, wherein the auxiliary information encoding unit is configured: - to estimate and to encode a flag of sudden change of power, as the auxiliary information, - when the flag indicates a predetermined mode, to estimate and to encode quantized transient power as the auxiliary information, wherein the auxiliary information contains only the flag and the quantized transient power, and - when the flag does not indicate the predetermined mode, to not include the quantized transient power in the auxiliary information, and the auxiliary information contains only the flag; wherein the audio signal comprises a frame having a plurality of sub frames, and the quantized transient power is estimated from the sub frame corresponding to a position of a sudden change of power; and wherein the auxiliary information encoding unit is further configured: - to use the sudden change of power as a position of a transient in the frame, - to perform a quantization of the transient power corresponding to the position of the transient in the frame to obtain the quantized transient power, and - to calculate the auxiliary information from two or more frames selected from frames that are earlier or later by one or more frames than the audio encoding target frame. an audio encoding unit for encoding an audio encoding target frame of the plurality of frames of the audio signal; and an auxiliary information encoding unit for estimating and encoding auxiliary information about a temporal change of power of the audio signal, the auxiliary information being used in packet loss concealment in decoding of the audio signal, wherein the auxiliary information encoding unit is configured: - to estimate and to encode a flag of sudden change of power, as the auxiliary information, - when the flag indicates a predetermined mode, to estimate and to encode quantized transient power as the auxiliary information, wherein the auxiliary information contains only the flag and the quantized transient power, and - when the flag does not indicate the predetermined mode, to not include the quantized transient power in the auxiliary information, and the auxiliary information contains only the flag; - to estimate and to encode a flag of sudden change of power, as the auxiliary information, - when the flag indicates a predetermined mode, to estimate and to encode quantized transient power as the auxiliary information, wherein the auxiliary information contains only the flag and the quantized transient power, and - when the flag does not indicate the predetermined mode, to not include the quantized transient power in the auxiliary information, and the auxiliary information contains only the flag; wherein the audio signal comprises a frame having a plurality of sub frames, and the quantized transient power is estimated from the sub frame corresponding to a position of a sudden change of power; and wherein the auxiliary information encoding unit is further configured: - to use the sudden change of power as a position of a transient in the frame, - to perform a quantization of the transient power corresponding to the position of the transient in the frame to obtain the quantized transient power, and - to calculate the auxiliary information from two or more frames selected from frames that are earlier or later by one or more frames than the audio encoding target frame. - to use the sudden change of power as a position of a transient in the frame, - to perform a quantization of the transient power corresponding to the position of the transient in the frame to obtain the quantized transient power, and - to calculate the auxiliary information from two or more frames selected from frames that are earlier or later by one or more frames than the audio encoding target frame.