There is disclosed a packet transmission apparatus for transmitting in a packet form a transmission unit including a data string arranged so as to divide predetermined data into a plurality of blocks, each block having a fixed length, block information for specifying the block type being added to each block. A DIF data processing circuit generates a transmission header having a new identifier by deleting predetermined redundancy information from the block information belonging to the plurality of blocks based on inputted data string, and then, generates a transmission unit having the generated transmission header. Next, a transmission terminal unit transmits the generated transmission unit by way of a transmission line. In this case, the DIF data processing circuit generates a new identifier by making the information of one block represent the information of the plurality of blocks to generate a transmission header having the generated identifier, or making the information of one block represent the information of an identical block or deleting the redundancy information including at least one of reserved data and invalid data.