Provided are a battery class determination device and a battery class determination method, allowing the class of a lead storage battery to be determined with high accuracy. This battery class determination device comprises a sensor unit for detecting a terminal voltage and a charge-discharge current of the lead storage battery, an internal resistance calculation unit for calculating a direct current internal resistance of the lead storage battery on the basis of the terminal voltage and the charge-discharge current detected by the sensor unit, and a class determination unit for determining the class of the lead storage battery on the basis of the calculated direct current internal resistance. When switching from a discharging control to a charging control of the lead storage battery, or, when switching from the charging control to the discharging control of the lead storage battery, the internal resistance calculation unit calculates the direct current internal resistance of the lead storage battery in a first period (T1) prior to the switching, and the direct current internal resistance of the lead storage battery in a second period (T2) after the switching. The class determination unit determines the class of the lead storage battery on the basis of the direct current internal resistance in the first period prior to the switching and the direct current internal resistance during the second period after the switching.