A transmission request for encoded data necessary to obtain a desired image is received (S801). It is determined whether the upper limit value of the data quantity of encoded data of a tile to be sent back in response to the transmission request is designated (S802). When the upper limit value is designated, encoded data of tiles to be sent back are referred to in a desired tile order. Of data of logical units which form the encoded data of a tile to be referred to, data of a logical unit corresponding to the transmission request and header data of the logical unit are output to a memory. The data size is counted in an output order, and a data group which is output until the counting result exceeds the upper limit value is sent back (S806 and S807).