A data transmission device is provided including a monitoring unit 2 for monitoring a transmission time period of data and predicting a transmission timing with which the above-mentioned data will be transmitted next time from the transmission time period. The data transmission device delays the transmission timing of data in the data transmission device when the transmission timing of the data in the data transmission device is close to a transmission timing predicted by the monitoring unit 2, whereas commands a network I/F unit 1 to transmit the data in the data transmission device when the transmission timing of the data in the data transmission device is not close to the predicted transmission timing.