This invention converts Packbit-encoded data into new Packbit-encoded data which allows to have a throughput=M. a extraction unit separates inputted encoded data into length information and data information, and outputs them to a conversion unit. The conversion unit has a count unit which cumulatively counts the number of output data after decoding indicated by the separated length information. The conversion unit divides length information of interest into first length information and second length information as needed, outputs the first length information, and sets the second length information as an initial count target to be counted by the count unit, so that the counted number N of output data reaches the throughput=M. The conversion unit combines the generated length information and the separated data information, and outputs new Packbit-encoded data.