A degradation degree assessment device for a secondary battery (2, 21, 22, 23, 24, 25, 26, 27) to assess a degree of degradation of the secondary battery, the degradation degree assessment device comprising: a battery characteristic acquisition unit configured to acquire a battery characteristic, which relates to a transition of a battery state in a predetermined voltage section of the secondary battery; and an assessment unit configured to assess the degree of degradation of the secondary battery based on the battery characteristic, which is acquired by the battery characteristic acquisition unit, or based on a battery characteristic-related value, which is computed based on the battery characteristic, wherein the battery characteristic includes a discharge voltage characteristic and/or a charge voltage characteristic, the discharge voltage characteristic is based on a voltage transition after the secondary battery is discharged to the discharge target voltage and stops being discharged, the charge voltage characteristic is based on a voltage transition after the secondary battery is charged to the charge target voltage and stops being charged, and the voltage transition is computed based on at least one of: a section capacity of the secondary battery in the voltage section; a rate of a voltage change of the secondary battery with respect to a capacity change of the secondary battery in the voltage section; a rate of a voltage change of the secondary battery with respect to an elapsed time in the voltage section; and a capacity ratio of the section capacity in the voltage section with respect to a total discharge capacity in a case of discharge to the discharge target voltage and/or with respect to a total charge capacity in a case of charge to the charge target voltage. a battery characteristic acquisition unit configured to acquire a battery characteristic, which relates to a transition of a battery state in a predetermined voltage section of the secondary battery; and an assessment unit configured to assess the degree of degradation of the secondary battery based on the battery characteristic, which is acquired by the battery characteristic acquisition unit, or based on a battery characteristic-related value, which is computed based on the battery characteristic, wherein the battery characteristic includes a discharge voltage characteristic and/or a charge voltage characteristic, the discharge voltage characteristic is based on a voltage transition after the secondary battery is discharged to the discharge target voltage and stops being discharged, the charge voltage characteristic is based on a voltage transition after the secondary battery is charged to the charge target voltage and stops being charged, and the voltage transition is computed based on at least one of: a section capacity of the secondary battery in the voltage section; a rate of a voltage change of the secondary battery with respect to a capacity change of the secondary battery in the voltage section; a rate of a voltage change of the secondary battery with respect to an elapsed time in the voltage section; and a capacity ratio of the section capacity in the voltage section with respect to a total discharge capacity in a case of discharge to the discharge target voltage and/or with respect to a total charge capacity in a case of charge to the charge target voltage. a section capacity of the secondary battery in the voltage section; a rate of a voltage change of the secondary battery with respect to a capacity change of the secondary battery in the voltage section; a rate of a voltage change of the secondary battery with respect to an elapsed time in the voltage section; and a capacity ratio of the section capacity in the voltage section with respect to a total discharge capacity in a case of discharge to the discharge target voltage and/or with respect to a total charge capacity in a case of charge to the charge target voltage.