In a method for adjusting a device voltage of a power storage device, when this device is represented as an equivalent circuit in which a parallel circuit of a capacitive device component and a short-circuit resistance indicating a magnitude of self-discharge of the device component is connected in series with a DC resistance of the power storage device, the power storage device has a property that, while the power storage device is pressed under a load and the device component is charged to generate a component voltage, the component voltage lowers when the load is reduced, but rises when the load is increased. The method includes a) component-voltage changing by load change of changing the load applied to the power storage device under a first load, generating a first component voltage in the device component, from the first load to change the component voltage from the first component voltage.