EARTH LEAKAGE DETECTING DEVICE, AND VEHICULAR POWER SUPPLY SYSTEM

To carry out a failure diagnose of a leakage detecting device highly precisely, first voltage an output unit (11a, OP1) generates a cyclic voltage that changes cyclically, and applies the cyclic voltage to the other end of a coupling capacitor (Cc) via a first resistance (R1). A second resistance (R2) and a third resistance (R3) are connected in series between a node and a second voltage output unit (11e, OP3), the node being between the coupling capacitor (Cc) and the first resistance (R1). A voltage measurement unit (11b) measures a voltage at a voltage dividing point between the second resistance (R2) and the third resistance (R3). In a period in which two types of fixed voltages are applied to the voltage dividing point in order, a diagnosing unit (11d) determines whether the leakage detecting device (10) is in a normal state, based on the voltage measured by the voltage measurement unit (11b).