Provided is an audio encoding device capable of improving performance of an adaptive codebook and improving quality of a decoded audio. In this audio encoding device, an adaptive codebook cuts out a vector specified by a comparator from adaptive code vectors stored in an internal buffer and outputs it to a filter and a switch. The filter performs a predetermined filtering process on the adaptive sound source signal and outputs the obtained adaptive code vector to the switch. According to an instruction from the comparator, the switch outputs the adaptive code vector directly output from the adaptive codebook to a adjuster when the adaptive codebook is searched and outputs the adaptive code vector output from the filter after being subjected to the filtering process to the gain adjuster when a fixed sound source is searched after the adaptive sound source search.