A battery management system which can output a battery state enabling optimum charge and discharge control to be performed even when a temperature variation occurs among individual single cells. A plurality of temperature sensors measure temperature values of a battery. A measurement unit measures a voltage and a current of the battery. A maximum/minimum temperature selection unit in a calculation unit determines a maximum temperature and a minimum temperature from the temperature values measured by the temperature sensors. An available power calculation unit calculates respective values of maximum available charge and discharge powers or maximum available charge and discharge currents of the battery corresponding to the maximum temperature and the minimum temperature based on the voltage and the current of the battery. A selection unit selects and outputs smaller maximum available charge and discharge powers or smaller maximum available charge and discharge currents from the respective values of the maximum available charge and discharge powers or the maximum available charge and discharge currents of the battery corresponding to the maximum temperature and the minimum temperature, which are calculated by the calculation unit.