To provide a time-division data transmitter/receiver capable of preventing the delay of a control operation or the execution of any erroneous control operation by changing an operation mode for respective transmission data contents.

This time-division data transmitter/receiver for transmitting and receiving a data packet in a TDMA/TTD communication system is provided with a transmitting/receiving part for transmitting/receiving a high frequency signal, a modulator/demodulator for converting the high frequency signal into a base band signal, and a vase band signal processor 1 for processing the base band signal. In this case, the data packet is added with a frame flag for designating the data packet, and a retry flag for designating the necessary/unnecessity of the re-transmission of the data packet when any communication error is generated in the data packet. At the time of transmitting the data packet by designating the retry flag of one data packet as the necessity of re-transmission, the base band signal processor 1 is switched and set to an operation mode in which one data packet is re-transmitted as long as the designation of the frame flag of the data packet received just after being transmitted or as long as any communication error is generated in the data packet.