A first communication device determines whether a remaining amount of a buffer that stores therein information included in reception data is equal to or less than a predetermined amount, and inserts, upon being determined that the remaining amount of the buffer is equal to or less than the predetermined amount, a transmission control signal for controlling data transmission performed by a second communication device into an idle section of data transmitted to the second communication device. The data includes a data section with information and the idle section without information. The data into which the transmission control signal is inserted is transmitted to the second communication device. The second communication device receiving the data, detects the transmission control signal in the idle section of the data and controls the data transmission based on the detected transmission control signal.