A battery state estimating device being one aspect of the present invention detects a current and a terminal voltage of a secondary battery, estimates a terminal voltage of the secondary battery which is based on a predetermined battery model by using measured values I(k) and V(k) respectively of the detected current and the detected terminal voltage, and sequentially identifies a parameter φ̂(k) of the battery model in such a way that the difference between a value based on the measured value of the terminal voltage and an estimate value of the terminal voltage converges to zero. Then, when a certain parameter φn in the identified parameter is equal to or larger than a predetermined first threshold δ1, the battery state estimating device performs upper limit processing of setting the value of the certain parameter φn to the first threshold δ1.