A storage amount estimation device estimates the storage amount of the energy storage device in which at least one of a positive electrode and a negative electrode contains an active material, at least two electrochemical reactions being generated in the active material depending on a transition of charge-discharge, the hysteresis between a storage amount-voltage value charge characteristic and a storage amount-voltage value discharge characteristic during generation of one of the electrochemical reactions being smaller than the hysteresis during generation of the other electrochemical reaction in the active material. The storage amount estimation device includes an estimator that estimates the storage amount using a voltage reference storage amount-voltage value characteristic obtained based on the storage amount-voltage value discharge characteristic when the one electrochemical reaction is generated more than the other electrochemical reaction.