A control device calculates an amount of increase ΔAm in freezing temperature measurement value Am from an initial freezing temperature Δ0 and calculates an amount of lowering in capacity corresponding to the amount of increase ΔAm in freezing temperature as an amount of lowering in capacity ΔBx due to deterioration of a material. The control device calculates an amount of lowering in capacity measurement value Bm from an initial capacity B0 as a whole amount of lowering in capacity ΔBm and calculates a material deterioration ratio X by using ΔBx and ΔBm. The control device calculates a value resulting from subtraction of ΔBx from ΔBm as an amount of lowering in capacity ΔBy due to precipitation of Li and calculates an Li precipitation deterioration ratio Y by using ΔBy and ΔBm.