A battery control device for controlling a storage battery system consisting of a plurality of storage batteries (1a, 1b) connected in parallel, the battery control device comprising: a temperature detecting unit (2a, 2b) to detect a temperature of each of the storage batteries (1a, 1b); an energy amount detecting unit (41a, 41b) to detect an energy amount of each of the storage batteries (1a, 1b); a control unit (42a, 42b) to calculate a deterioration rate of each of the storage batteries (1a, 1b) connected in parallel based on the temperature detected by the temperature detecting unit (2a, 2b) and the energy amount detected by the energy amount detecting unit (41a, 41b), and to control the amount of power to be input to or output from each of the storage batteries (1a, 1b) connected in parallel so that the deterioration rates of the storage batteries are close to each other, characterized by a first calculation unit adapted to calculate, with respect to a first storage battery out of the plurality of storage batteries (1a, 1b) connected in parallel, a first deterioration rate DTa based on the temperature and a second deterioration rate DSa based on the energy amount, and a second calculation unit adapted to calculate, with respect to a second storage battery different from the first storage battery, a first deterioration rate DTb based on the temperature and a second deterioration rate DSb based on the energy amount, wherein the control unit (42a, 42b) is adapted to calculate such energy amount that satisfies the equation (DTa × DSa) = (DTb × DSb) as a target energy amount (Sa, Sa', Sb, Sb') with respect to the first storage battery and/or the second storage battery, and to control the amount of power to be input to or output from the first storage battery and/or the second storage battery in order for the first storage battery and/or second storage battery to attain the target energy amount. a temperature detecting unit (2a, 2b) to detect a temperature of each of the storage batteries (1a, 1b); an energy amount detecting unit (41a, 41b) to detect an energy amount of each of the storage batteries (1a, 1b); a control unit (42a, 42b) to calculate a deterioration rate of each of the storage batteries (1a, 1b) connected in parallel based on the temperature detected by the temperature detecting unit (2a, 2b) and the energy amount detected by the energy amount detecting unit (41a, 41b), and to control the amount of power to be input to or output from each of the storage batteries (1a, 1b) connected in parallel so that the deterioration rates of the storage batteries are close to each other, characterized by a first calculation unit adapted to calculate, with respect to a first storage battery out of the plurality of storage batteries (1a, 1b) connected in parallel, a first deterioration rate DTa based on the temperature and a second deterioration rate DSa based on the energy amount, and a second calculation unit adapted to calculate, with respect to a second storage battery different from the first storage battery, a first deterioration rate DTb based on the temperature and a second deterioration rate DSb based on the energy amount, wherein the control unit (42a, 42b) is adapted to calculate such energy amount that satisfies the equation (DTa × DSa) = (DTb × DSb) as a target energy amount (Sa, Sa', Sb, Sb') with respect to the first storage battery and/or the second storage battery, and to control the amount of power to be input to or output from the first storage battery and/or the second storage battery in order for the first storage battery and/or second storage battery to attain the target energy amount.