A first upper limit and a second upper limit of emission power are set in each of the NaS batteries. The second upper limit is maximum value of the emission power for maintaining the temperature of the NaS battery at an upper limit temperature or less. In allocation of the emission power to each of the NaS batteries, each of the NaS batteries is separated into a preferential virtual battery to which a non-excess of the emission power that does not exceed the second upper limit is allocated and non-preferential virtual battery to which an excess of the emission power that exceeds the second upper limit is allocated, and after the emission power is allocated to all the preferential virtual batteries, the emission power is allocated to each of the non-preferential virtual batteries.