A storage amount estimation device is provided that can estimate a storage amount of an energy storage device containing an active material in which a storage amount-voltage characteristic exhibits a hysteresis, an energy storage module including the storage amount estimation device, a storage amount estimation method, and a computer program. An energy storage device contains an active material exhibiting hysteresis between a storage amount-voltage charge characteristic and a storage amount-voltage discharge characteristic in a positive electrode and/or a negative electrode, the active material generating a plurality of electrochemical reactions according to transition of charge-discharge. A BMU includes an acquisition unit that acquires a storage amount-voltage charge characteristic for reference and/or a storage amount-voltage discharge characteristic for reference based on the first characteristic, the second characteristic, and voltage history of the charge-discharge and an estimation unit that estimates the storage amount based on the voltage history of the charge-discharge, the third characteristic and/or the fourth characteristic, and the acquired voltage.