To provide a high speed sub-band division device with satisfactory conversion efficiency.

An inputted image signal s10 is connected with a sub-band division filter 11 which performs sub-band division in the horizontal direction at the first stage, output s11-1 of low frequency components of the sub-band division filter is connected with a sub-band division filter 12 which performs sub-band division in the horizontal direction at the next stage and on the other hand, output s11-2 of high frequency components of the sub-band division filter 11 is connected with a memory 14 which stores a sub-band division result in the horizontal direction. Output of a sub-band division filter at the second stage is also performed similarly as that of the sub-band division filer at the first stage. Thus, the sub-band division in the horizontal direction of n stages is performed by cascading n stages of sub-band division filers. In addition, output of the memory 14 is connected with a sub-band division filer 15 which performs sub-band division in the vertical direction at the first stage, processing similar to the sub-band division in the horizontal direction is performed and the high frequency components are outputted to the outside.