An ECU obtains an OCV and an internal pressure, obtains a first estimated value of an SOC corresponding to the time of charging and a second estimated value of the SOC corresponding to the time of discharging using the obtained OCV and a first correspondence, obtains a third estimated value of an SOC corresponding to the time of charging and a fourth estimated value of the SOC corresponding to the time of discharging using the obtained internal pressure and a second correspondence, estimates the SOC using at least one of the first or the third estimated value when a first difference between the first and the third estimated value is less than a second difference between the second and the fourth estimated value, and estimates the SOC using at least one of the second or the fourth estimated value when the second difference is less than the first difference.