To provide an earth fault detector capable of detecting surely disconnection in a route from an earth detecting means including a coupling capacitor up to a direct current power source, in the earth detector for detecting grounding generated in at least either of the direct current power source or a load connected thereto.

This earth fault detector of the present invention is constituted of a high-voltage battery, an inverter circuit, an alternating current motor, a system main relay, an earth detecting circuit, the coupling capacitor, and a disconnection detecting circuit. After the system main relay connects the high-voltage battery to the inverter circuit, a level of a voltage in a connection point between the earth detecting circuit and the coupling capacitor is compared with a voltage of a prescribed disconnection determination reference power source, by the disconnection detecting circuit. The disconnection is thereby detected in the route from the earth detecting circuit including the coupling capacitor up to the high-voltage battery.

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