It aims to provide the technique capable of reducing the process to be executed on the reception side and shortening the time from the occurrence of an error to the sending of a retransmission request. To achieve this, the image data is encoded in units of block by the encoding unit, the reference information representing whether or not the block is referred when another block is encoded is generated by the reference map generation unit, and then the encoded block and the reference information are transmitted by the transmission unit.