In a method for adjusting a nickel-metal hydride storage battery, based on a correlation between a charge amount after valve opening and an increased amount of a discharge reserve capacity which are previously ascertained, the charge amount after valve opening corresponding to a target value of the set increased amount of the discharge reserve capacity is calculated and this calculated value is set as a target charge amount after valve opening. In a discharge reserve adjusting step, when a charge amount of the battery from the time when a safety valve device is opened after start of overcharge of the battery reaches the set target charge amount after valve opening, overcharge of the battery is terminated.