To provide an audio signal encoding device and an audio signal decoding device which are improved by reducing the deterioration in sound quality.

An audio signal is divided to a plurality of sub-band signals for each prescribed frequency band by a band dividing part 101, a number of quantized bits is determined by calculating the energy of each of sub-band signals by an allocation bit calculating part 102 and on the basis of this number of quantized bits, each of sub-band signals is quantized by a quantizing part 103. In a code book generating part 104, an index number showing a pattern in the number of allocation bits for each of sub-band signals is extracted and in a bit stream generating part 105, one bit stream is generated by multiplexing the quantized sub-band signal and the index number. In an allocation bit information extracting part 106, the index number is extracted from this bit stream, the number of quantized bits is calculated from the index number by an allocation bit calculating part 107 and on the basis of this number of quantized bits, each of quantized sub-band signals is inversely quantized by an inverse quantizing part 108.