An object is to predict a deterioration state of a secondary battery even in an environment where temperature and a charging voltage change. A lifetime estimation device of the secondary battery includes a measuring unit for measuring the capacity of the secondary battery in the full charging state; a temperature sensing unit for sensing the ambient temperature of the secondary battery; and a storage unit for storing a table of a proportional coefficient corresponding to temperature in advance, and a predicted deterioration line of the secondary battery is calculated with the use of a nonlinear regression equation approximated to a measured deterioration line obtained by the measuring unit. The lifetime estimation device may construct a lifetime estimation system with the use of a neural network.