A secondary battery and a control section are included. An electrode of the secondary battery has a singular point at which a variation in an output voltage with respect to a capacity is singularly changed. The control section includes a detection section and a calculation setting section. The detection section changes the capacity of the secondary battery, and detects a singular point capacity which is the capacity at which the singular point appears. When the secondary battery is deteriorated, the calculation setting section calculates and sets at least one of an upper limit value and a lower limit value of the capacity by using a detection value of the singular point capacity after the deterioration so that a potential of the electrode does not deviate from a predetermined range.