To adjust the length of a bit stream while suppressing the missing quantity of information.

This bit stream adjustment device is provided with a reduction means that reduces the number of bits of some of n-sets of digital data, a setting means that generates additional bits whose number is less than the number of reduced bits and sets a logical value of the additional bits based on the value of the reduced bits, and an output means that inserts the additional bits to a bit stream not including the reduced bits to generate and output a new bit stream. The length of the bit stream can be adjusted by reducing the number of bits. Furthermore, since the additional bits to irreversibly hold information lost through the bit reduction are provided to the bit stream the missing information can be reproduced to some degree in the case of restoring the length of the bit stream to the original length.