An encoding device comprising: subband dividing means configured to divide an input signal into a plurality of subbands, and to generate a low-frequency subband signal made up of a plurality of subbands on the low-frequency side, and a high-frequency subband signal made up of a plurality of subbands on the high-frequency side; feature amount calculating means configured to calculate a feature amount that represents features of the input signal based on power within at least any one of the low-frequency subband signal of the input signal; smoothing means configured to subject the feature amount to smoothing; pseudo high-frequency subband power calculating means configured to calculate a pseudo high-frequency subband power that is an estimated value of power of the high-frequency subband signal based on the smoothed feature amount and a predetermined coefficient; selecting means configured to calculate a high-frequency subband power that is a power of the high-frequency subband signal from the high-frequency subband signal, and to compare the high-frequency subband power and the pseudo high-frequency subband power to select a coefficient from a plurality of coefficients, that approximates the high-frequency subband signal; high-frequency encoding means configured to encode coefficient information that represents the selected coefficient, and smoothing information relating to the smoothing to generate high-frequency encoded data; low-frequency encoding means configured to encode a low-frequency signal that is a low-frequency signal of the input signal to generate low-frequency encoded data; and multiplexing means configured to multiplex the low-frequency encoded data and the high-frequency encoded data to obtain an output code string; wherein the smoothing means subjects the feature amount to smoothing by performing weighted averaging for the feature amount of a predetermined number of continuous frames of the input signal; wherein the smoothing information is information that indicates at least one of the number of the frames used for the weighted averaging, or weight used for the weighted averaging; parameter determining means configured to determine at least one of the number of the frames used for the weighted averaging, or weight used for the weighted averaging based on the high-frequency subband signal. subband dividing means configured to divide an input signal into a plurality of subbands, and to generate a low-frequency subband signal made up of a plurality of subbands on the low-frequency side, and a high-frequency subband signal made up of a plurality of subbands on the high-frequency side; feature amount calculating means configured to calculate a feature amount that represents features of the input signal based on power within at least any one of the low-frequency subband signal of the input signal; smoothing means configured to subject the feature amount to smoothing; pseudo high-frequency subband power calculating means configured to calculate a pseudo high-frequency subband power that is an estimated value of power of the high-frequency subband signal based on the smoothed feature amount and a predetermined coefficient; selecting means configured to calculate a high-frequency subband power that is a power of the high-frequency subband signal from the high-frequency subband signal, and to compare the high-frequency subband power and the pseudo high-frequency subband power to select a coefficient from a plurality of coefficients, that approximates the high-frequency subband signal; high-frequency encoding means configured to encode coefficient information that represents the selected coefficient, and smoothing information relating to the smoothing to generate high-frequency encoded data; low-frequency encoding means configured to encode a low-frequency signal that is a low-frequency signal of the input signal to generate low-frequency encoded data; and multiplexing means configured to multiplex the low-frequency encoded data and the high-frequency encoded data to obtain an output code string; wherein the smoothing means subjects the feature amount to smoothing by performing weighted averaging for the feature amount of a predetermined number of continuous frames of the input signal; wherein the smoothing information is information that indicates at least one of the number of the frames used for the weighted averaging, or weight used for the weighted averaging; parameter determining means configured to determine at least one of the number of the frames used for the weighted averaging, or weight used for the weighted averaging based on the high-frequency subband signal.