A battery management unit capable of more reliably turning off a high-voltage relay. A battery management unit 1 includes a high-voltage relay 5 serving as a switch unit that turns on/off electrical connection between a high-voltage battery 102, which is a secondary battery, and an external device, and a power source IC 6 serving as a disconnection control unit having a first disconnection processing function of turning off the high-voltage relay 5 at the time of abnormality of the battery management unit 1 and a second disconnection processing function of detecting an abnormality of the first disconnection processing function and turning off the high-voltage relay 5.