A monitoring device includes a first detection block, a second detection block, and a monitoring unit. Each of the first detection block and the second detection block includes one or more voltage detectors that detect voltages across power storage cells. The monitoring unit includes a complement processor that, when a circuit in the first detection block breaks down and the first detection block fails to transmit the states of the power storage cells to the monitoring unit, complements the states of the power storage cells that have not been acquired from the first detection block, based on the states of the power storage cells detected in the second detection block.