A wiring device includes a leakage control unit for detecting a leakage current flowing through an electrical path connecting a commercial power supply and a load to perform a leakage determination and a switching unit for interrupting the electrical path in accordance with the leakage determination of the leakage control unit The leakage control unit has a filter for filtering the detected leakage, a square operation unit for calculating the square operation value of a signal which relates to the leakage current passing through the filter, and a threshold determination unit for performing the leakage determination in accordance with the square operation value obtained by the square operation unit. Consequently, the leakage determination is performed in accordance with the square operation value, so that the leakage can be detected with high accuracy even when the leakage current has a distorted waveform, and the electrical leakage can be reliably interrupted.