A an estimation arithmetic processing unit estimates an open circuit voltage and an internal resistance with respect to a charging rate of the secondary battery based on a charge-discharge voltage and a charge-discharge current of the secondary battery, and input-output power of the DC-AC converter, estimates efficiency of the DC-AC converter and power consumption of an auxiliary device of the DC-AC converter, and estimates charge-discharge energy efficiency with respect to the charging rate of the secondary battery and a rated input-output ratio on an AC side of the DC-AC converter based on the estimated open circuit voltage, the internal resistance, the efficiency of the DC-AC converter, and the power consumption of the auxiliary device of the DC-AC converter.