A packet transmitter for transmitting, in the form of a packet, a transmission unit including a data sequence which comprises fixed length blocks formed by dividing predetermined data and to each of which block information representing the type of block is added. A DIF data processing circuit (104) eliminates predetermined redundant information from block information belonging to a plurality of blocks in accordance with an inputted data sequence, generates a transmission header having a new identifier, and generates a transmission unit having the generated transmission header. Then, a transmission terminal (102) transmits the generated transmission unit through a transmission line. At this time, the DIF data processing circuit (104) generates a new identifier by permitting a predetermined set of block information to represent a plurality of sets of block information and generates a transmission header having the generated identifier, or permits one set of block information to represent the same block information, or eliminates redundant information which includes at least one of preliminary data and invalid data.