Abstract: A ground fault detection apparatus is used for an on-board system. The on-board system includes a power source unit, a power storage unit, a conductive path, and a disconnection unit. The conductive path includes a first conductive path, a second conductive path, and a third conductive path. The disconnection unit includes a first disconnection unit and a second disconnection unit. A second load is connected to one path out of the second conductive path and the third conductive path, and a third load is connected to the other path. The ground fault detection apparatus includes a detection unit (a current detection unit and a control circuit) configured to detect a ground fault on at least one of the second conductive path and the third conductive path.