NOVELTY - Two leakage detection switches are respectively connected to high and low voltage sides of a battery pack (70). A leakage detection resistor is connected to the battery pack via the switches, in which the midpoint of the resistor is connected to ground. A voltage detector senses leakage voltage values in the resistor. A calculator computes the output of the detector to detect the leakage. A controller turns the switches ON and OFF to detect a leakage voltage value (Vg), and turns them OFF and ON to detect another value such that the calculator detects leakage based on the values.    USE - Leakage detection circuit for detecting leakage of a power supply device that powers a motor for running an electric vehicle such as a hybrid car or an electric car.    ADVANTAGE - The voltage detector amplifies only the voltage difference such that the leakage resistance detection accuracy is not affected. As a result, it is possible to always accurately detect the leakage resistance. The leakage detection circuit detects leakage voltages at given points by use of one voltage detector. With this, an inexpensive and simple structure is provided to safely use the electric vehicle.    DETAILED DESCRIPTION - The calculator circuit detects a leakage resistance value R1 based on the following equation: R1=(Ra/(((Vh(t1))divide by(Vt(t1)))+((Vg(t2))divide by(Vt(t2)))))-(Ra+Rb)where Ra is the resistance value of two voltage detection resistors; Rb is the resistance value of two voltage dividing resistors; Vt(t1) is the total voltage value of the battery pack at timing t1 where the leakage detection switches are turned ON and OFF, respectively; Vh(t1) is the first of two leakage voltage values generated in the voltage detection resistor at the timing t1; Vt(t2) is the total voltage value of the battery pack at the timing t2 where the leakage detection switches are turned OFF and ON, respectively; and Vg(t1) is the second leakage voltage value generated in the second voltage detection resistor at the timing t2.    DESCRIPTION OF DRAWING(S) - The drawing shows a circuit diagram of the leakage detection circuit.    Resistance values (Ra,Rb)    Leakage voltage value (Vg)    Battery pack (70)    Batteries (71)    Voltage detection circuits (73)