An updated region encoding unit detects an updated region in a frame of an inputted image signal and encodes the updated region. A retransmission candidate tile extracting unit extracts from within a screen a tile which does not belong to an updated region in a current frame and which is a partial region transmitted after encoded with a quality equal to or less than a first quality. A character likelihood estimating unit, with respect to a tile extracted by the retransmission candidate tile extracting unit, calculates a likelihood value indicating likelihood that the tile is a character region. A character-likelihood-order intra update unit selects a tile in decreasing order of the likelihood value from among tiles extracted by the retransmission candidate tile extracting unit, and encodes the tile with a second quality which is higher than the first quality and transmits the result.