A performance deterioration detecting apparatus detects an initial state of sudden deterioration in performance of an energy storage device as a performance deterioration start state, and includes: a first acquiring unit configured to acquire a first maximum variation amount as a maximum value of a capacity variation amount that is a degree of variation in current carrying capacity relative to variation in voltage of the charged or discharged energy storage device, regarding a capacity-voltage property at a first time point, indicating relation between the capacity variation amount and the voltage; a second acquiring unit configured to acquire a second maximum variation amount as a maximum value of the capacity variation amount regarding the capacity-voltage property at a second time point after the first time point; and a performance deterioration determiner configured to determine that the energy storage device is in the performance deterioration start state at the second time point if a variation amount ratio as a ratio of the second maximum variation amount to the first maximum variation amount exceeds a predetermined value.