A post-deterioration performance estimating apparatus estimates a post-deterioration performance value indicating performance of an energy storage device at a predetermined deterioration point, wherein discharge capacity of the energy storage device discharging at a predetermined first current is referred to as energy storage capacity, discharge capacity of the energy storage device discharging at a second current of a current value smaller than that of the first current is referred to as small current discharge capacity, a relational expression on relation among initial capacity of the energy storage device, a first capacity decreased amount obtained by subtracting the small current discharge capacity from the initial capacity, a second capacity decreased amount obtained by subtracting the energy storage capacity from the small current discharge capacity, and a cumulative operating period as a cumulative value of operating periods of the energy storage device is referred to as a first relational expression, and the post-deterioration performance estimating apparatus includes a post-deterioration performance estimator configured to estimate the post-deterioration performance value at the deterioration point in accordance with the first relational expression and the cumulative operating period at the deterioration point.