A leakage current detection device coupled to AC power supply wires carrying an AC signal, which includes: a leakage current detection circuit including a leakage current detector, the leakage current detection circuit operating during first half-cycles among positive and negative half-cycles of the AC signal to detect a leakage current of the power supply wires and to disconnect the power supply wires from an output side when a leakage current exceeding a first threshold value is detected; and a self-detecting circuit coupled to the leakage current detection circuit, operating during second half-cycles among the positive and negative half-cycles of the AC signal to test whether the leakage current detection circuit is functioning normally.