A battery pack includes a plurality of modules connected in series to one another. Each of the plurality of modules includes a plurality of cells connected in parallel to one another. If a first condition and a second condition are satisfied, an ECU diagnoses an abnormality in which a current path of a cell included in any module breaks. The first condition is a condition that the voltage difference between the maximum voltage and the minimum voltage among a plurality of voltage values is less than a reference value before execution of plug-in charging control, each of the plurality of voltage values being detected by a corresponding one of a plurality of voltage sensors. The second condition is a condition that the voltage difference between the maximum voltage and a voltage is more than or equal to the reference value after execution of the plug-in charging control.