A lead-acid battery monitoring device includes a plurality of sensor units 20 attached to a plurality of lead-acid batteries 1 connected in series and/or in parallel and a control unit 10 that sequentially establishes wireless communication connection with the plurality of monitoring units 20. The lead -acid battery monitoring device executes a first monitoring operation in which the management unit 10 sequentially receives monitoring data including an internal resistance and a temperature of each lead-acid battery 1 from the plurality of monitoring units 20 and a second monitoring operation in which the management unit 10 sequentially receives monitoring data including the temperature of each lead-acid battery 1 from the plurality of monitoring units 20.