To provide a leakage detection device for preventing an adopting operation without disturbing a leakage detecting operation in a high sensitivity operating area since a power failure or an unnecessary caution caused by an unnecessary adopting operation by an adopted current caused by power source side grounding may become an obstacle in production.

A cable-run to ground voltage, which may cause an adopting operation, generated between a transformer class-B ground phase of a monitored cable way and a class-D or class-C ground pole or a ground structure of an electric facility connected thereto is monitored and while defining this voltage as a criterion, a phase of a leaked current detected by a zero-phase current transformer is determined. In the case where the leaked current is an adopted current from a load side L of the detection zero-phase current transformer to a power source side K, namely, a transformer side and the cable-run to ground voltage exceeds an appropriately settled operation sensitivity voltage settlement value, an output control circuit for stopping an output operation of the leakage detection device is added, thereby preventing an unnecessary operation caused by an adopted current without disturbing the high sensitivity operation area of the leakage detection device.