A communication apparatus is connected to another communication apparatus via a power source line, a signal line, and a shared line. The communication apparatus includes a detector and a communicator. The detector detects the phase of an alternating-current voltage applied between a first terminal for connecting to the power source line and a second terminal for connecting to the shared line. The communicator communicates with the other communication apparatus by executing at least one of transmission or reception of an electric current signal generated by opening and closing a circuit including the signal line and the shared line except when the phase detected by the detector is within a specific range. The specific range is defined as a range in which an induced electric current flowing through the signal line due to the alternating-current voltage is greater than a reference value.