A signal encoding apparatus (10) limits an inputted time series signal to a low frequency band signal having a certain cut-off frequency or less to include the low frequency band signal into code train for outputting encoded low frequency band code train. In addition, the signal encoding apparatus (10) adaptively determines aliasing frequency fa, shift frequency fsh or tone•noise synthesis information r used for generation of high frequency band signal at the decoding side to include these information into code train outputted along with high frequency band spectrum envelope information as high frequency band generation information. A signal decoding apparatus generates a high frequency band signal from a low frequency band signal by using high frequency band signal generation information included in code train and high frequency band spectrum envelope to add the generated high frequency band signal and the low frequency band signal to thereby output a time series signal extended up to the high frequency band signal.