<p>A signal coupler for power line communication where a signal is taken out or injected through a capacitor (3) electrostatically coupled with a power line (1) comprises an insulator (11) having one end provided with an upper terminal (2) electrically connected with the power line (1) and the other end provided with a cavity (11a) opening to the other end side, a capacitor (3) buried in the insulator (11) while electrically connected with the upper terminal (2), and a protective circuit (4) contained in the cavity (11a) and connected in series with the capacitor (3) in order to protect it against abnormal voltage and to perform input/output impedance matching wherein the protective circuit (4) is removable.</p>
