A communication system including a transmission device and a reception device is provided. A processor of the transmission device is configured to store image data on a transmission buffer after deleting all the stored image data in a case in which a first condition and a second condition are met. The processor is configured to store the image data without deleting the stored image data in a case in which at least one of the first condition and the second condition is not met. The first condition indicates that a second transmission-completion frame this time is after a previous first transmission-completion frame. The second condition indicates that a third transmission-completion frame is not the next frame of the transmission-completion second frame. The third transmission-completion frame is a frame of the image data to be stored after confirming the transmission-completion frame this time.