A communication system includes a first communication device that transmits transmission data containing user data and control data, and a second communication device that receives the transmission data from the first communication device. The second communication device includes a temporary storing unit that temporarily stores therein the received transmission data, and a space-insufficient-information transmitting unit that transmits, when an amount of the transmission data stored in the temporary storing unit exceeds a first threshold, space insufficient information indicating that available storage space of the temporary storing unit is insufficient to the first communication device. The first communication device includes a transmission control unit that transmits, when receiving the space insufficient information from the second communication device, transmission data excluding the user data from the transmission data to the second communication device, and that resumes, when receiving space-insufficient dissolution information from the second communication device, transmission of the user data.