Cell voltage measurement is executed immediately after termination of diagnosis on a cell voltage detection function. In a battery managing device 10, a voltage detecting unit 140 detects a terminal voltage of each of battery cells 21 and 22. An RC filter 110 is electrically connected to voltage detecting lines L1, L2, and L3, and a status variation causing unit 130 causes an electrical status variation with respect to the voltage detecting lines L1, L2, and L3. A voltage fluctuating unit 120 fluctuates the terminal voltage of the battery cells 21 and 22 in response to the electrical status variation that is caused by the status variation causing unit 130. A microcomputer 150 diagnoses the voltage detecting unit 140 on the basis of a detection result of the terminal voltage of the battery cells 21 and 22 by the voltage detecting unit 140 when the terminal voltage of the battery cells 21 and 22 is fluctuated by the voltage fluctuating unit 120.