STATE OF CHARGE CALCULATION DEVICE

PROBLEM TO BE SOLVED: To provide a state of charge calculation device capable of easily obtaining the state of charge of a secondary battery.SOLUTION: The state of charge calculation device comprises: a transformer determining current outputted from the other terminal of a second winding in accordance with a winding ratio of a first winding and the second winding and current flowing through a secondary battery; a first voltmeter measuring a voltage across the secondary battery; a second voltmeter measuring a voltage value across a resistor; a calculation unit. The calculation unit includes the steps of: obtaining a first voltage value across the secondary battery and a second voltage value across the resistor measured respectively by the first voltmeter and the second voltmeter, for each unit time of a period from the completion of charging using an external charging device to the start of charging using the next external charging device; obtaining a current value by dividing the first voltage value by a value obtained by multiplying a resistance value of the resistor prestored on a storage unit by a preset value determined by the winding ratio of the transformer; obtaining electric power by multiplying the second voltage value by the current value for each unit time; and obtaining the state of charge of the secondary battery by accumulating the electric power obtained for each period.