To provide a packet communicating apparatus that can reduce a padding area. A packet communicating apparatus used in a high speed packet communication in a radio mobile communication network includes: an SDU.fwdarw.PDU divider for dividing packet data to be transmitted to an opposite entity, into protocol data units; and a synchronous control signal generator 223 for jointly putting a control signal to change a protocol data unit length, on a padding area of a protocol data unit occurring at a time of the division.