NOVELTY - A conversion circuit (C11) converts the voltage of ends of a secondary battery (B1) into electric current. A resistance (R21) converts the electric current into the voltage which makes the negative-electrode potential of a battery (B2) as reference. The negative-electrode potential of battery (B4) is converted into reference by repeating current and voltage conversions for the voltage of batteries (B1-B3). The positive-electrode potential of battery (B4) is converted into reference by repeating current and voltage conversions for the voltage of batteries (B5-B7).    USE - For battery pack mounted on hybrid vehicle and electric vehicle.    ADVANTAGE - Since the voltage of the secondary batteries can be picked-out in a common intensive circuit, the number of high-voltage devices used for the interface to detect the battery voltage is reduced and the size of the voltage detector is reduced. The battery voltage is detected with a simple structure.    DETAILED DESCRIPTION - A voltage-current conversion circuit (C21) converts the voltage converted by the resistance (R21) into an electric current. A resistance (R31) converts the electric current into the voltage which makes the negative-electrode potential of secondary battery (B3) as reference. A conversion circuit (C31) converts the voltage converted by the resistance (R31) into an electric current. A resistance (R41) converts the electric current into the voltage which makes the negative-electrode potential of secondary battery (B4) as reference. The negative-electrode potential of battery (B4) is converted into reference by repeating current and voltage conversions for the voltage of batteries (B1-B3). The positive-electrode potential of battery (B4) is converted into reference by repeating current and voltage conversions for the voltage of batteries (B5-B7).    DESCRIPTION OF DRAWING(S) - The figure shows a circuit diagram of the voltage detector of the battery pack. (Drawing includes non-English language text)    Battery pack (10)    Voltage detection circuit (30)    Secondary batteries (B1-B7)    Voltage-current conversion circuits (C11-C77)    Resistances (R21-R67)