To reduce the effect of a quantization error caused after decoding in the case of coding/decoding to realize multi-channel processing due to extension by the new standard while enabling reproduction by the reproduction device having provision for the old standard is made available.

A device has an adaptive channel conversion circuit 202a that multiplies a 1st coefficient with a signal of either left(L) or right(R) channel, multiplies a 2nd coefficient with the other channel, applies channel mixture processing that mixes the signal of the channel multiplied with the 2nd coefficient to the signal of the channel multiplied with the 1st coefficient to both the L, R channels and generates signals (L+R)/2 and (L-R)/2 from the L, R channels after the channel mixture processing, has a 1st coding circuit 202b that encodes the (L+R)/2 with a CODEC A and has a 2nd coding circuit 202c that encodes the (L-R)/2 with a CODEC B.