A communication system includes a transmission device that transmits an information signal having information defined as a binary state value, the transmission device including a signal generation unit that generates an information decryption signal to transmit the information decryption signal together with the information signal, wherein the state value of the information decryption signal is unchanged when the state value of the information signal is changed, whereas the state value of the information decryption signal is changed when the state value of the information signal is unchanged; and a reception device that receives the information signal and the information decryption signal, the reception device including an information acquisition unit that acquires the state value of the information signal based on a changing timing of the state value of each of the information signal and the information decryption signal received.