An impedance measuring device outputs an alternating current of a prescribed frequency to a positive electrode terminal and a negative electrode terminal of the laminated type battery. The impedance measuring device detects an alternating-current potential difference between the positive electrode terminal and an intermediate-point terminal, and an alternating-current potential difference between the negative electrode terminal and the intermediate-point terminal. The impedance measuring device adjusts an amplitude of the alternating current such that the alternating-current potential difference between the positive electrode terminal and the intermediate-point terminal, and the alternating-current potential difference between the negative electrode terminal and the intermediate-point terminal coincide. The impedance measuring device computes an impedance of the laminated type battery on the basis of the alternating current adjusted and the alternating-current potential difference. On the a phase difference between an alternating-current potential generated at the positive electrode terminal and an alternating-current potential generated at the negative electrode terminal, or a parameter related to the phase difference, the impedance measuring device performs any one process of: a diagnosis process for diagnosing whether or not a measurement state is defective; a cancellation process for discarding a measurement result; and a hold process for fixing the measurement result at a prescribed value.