To provide a DC earth fault detecting device capable of automatically detecting a circuit in which earth fault occurs, and a DC earth fault detecting method.

The DC earth fault detecting device includes a ground circuit 5, an earth fault detecting circuit 6 for detecting an earth fault current, and an earth fault determination circuit 7 for determining a cut-off section 24 where the earth fault has occurred. The earth fault detecting circuit 6 outputs a value proportional to a variation per unit time of current flowing the cut-off section 24, as a detection value. The earth fault determination circuit 7 has a determination part 72 for determining the cut-off section 24 provided with the earth fault detecting circuit 6 in which a detection value that is the maximum in all the detection values detected from the earth fault detecting circuit 6, has been detected, as a cut-off section 24g where the earth fault has occurred.