A secondary-battery monitoring device includes: a use-state memory device that stores a transition of a load parameter indicating a use state of a secondary battery; and a battery capacity prediction device that predicts a temporal change of a battery capacity of the secondary battery on the basis of a prediction function. The prediction function is derived from a relation between growth of a film formed in an electrode surface of the secondary battery and a reduction of a precursor component of the film which is contained in an electrolyte of the secondary battery. The battery capacity prediction device determines a coefficient of the prediction function on the basis of the transition of the load parameter which is stored in the use-state memory device, and predicts the temporal change of the battery capacity of the secondary battery on the basis of the prediction function which uses the coefficient.