A parameter estimation device using a filter includes a preprocessing computing circuit, a state estimating circuit and a state-of-charge estimating circuit. A low-pass filter of the preprocessing computing circuit transfers the voltage preprocessing value and the current preprocessing value from inputted discharge-and-charge current value and terminal voltage value, respectively. The state estimating circuit estimates parameters of a state equation of a battery equivalent model based on the battery equivalent model containing a resistance and a capacitor from the voltage preprocessing value and the current preprocessing value inputted. The state-of-charge estimating circuit estimates the state of charge from state quantity obtained. The time constant varies in such a way that the higher the temperature and the state of charge becomes the smaller the time constant becomes.