EARTH LEAKAGE DETECTION DEVICE AND VEHICLE POWER SUPPLY SYSTEM

In order to quickly and accurately diagnose the failure of a coupling capacitor of an earth leakage detection device, voltage output unit (11a, OP1) generates a periodically changing periodic voltage and applies the periodic voltage to the other end of coupling capacitor (Cc) via first resistor (R1). Second resistor (R2) and third resistor (R3) are connected in series between a connection point between coupling capacitor (Cc) and first resistor (R1), and a predetermined fixed potential. Voltage measurement unit (11b) measures a voltage at a voltage dividing point between second resistor (R2) and third resistor (R3). Diagnosis unit (11d) determines whether or not coupling capacitor (Cc) is normal based on a voltage measured when switch (MRp, MRm, MRpp) is turned on in a state where voltage output unit (11a, OP1) outputs a fixed voltage.