According to one embodiment, a controller changes, when a charging state transitions from a first state of charging a first battery by using a power from an external power supply to a second state of charging the first battery by using a power from the second battery and if rated power of the external power supply and the rated discharge power of the second battery are different from each other, an upper limit of an input current to a charging circuit to a value corresponding to the rated discharge power of the second battery.