An energy storage device management method for deciding an SOC estimated value includes: preparing first and second SOC estimation methods for estimating an SOC; and employing a predetermined value as the SOC estimated value when a first SOC region and a second SOC region are different. V-SOC correlation between a voltage and the state of charge of the energy storage device is sectioned into a plurality of SOC regions. The first SOC region is the SOC region that the SOC estimated by the first SOC estimation method belongs to, and the second SOC region is the SOC region that the SOC estimated by the second SOC estimation method belongs to. The predetermined value is set to a value close to a boundary value on a side close to the first SOC region of boundary values sectioning the second SOC region, or a value between the boundary value and an intermediate value of the second SOC region.