To provide a capacitor device allowing preventive maintenance of cell deterioration to be reliably carried out while preventing excessive warning output.

The capacitor device includes a capacitor group 11 having a plurality of capacitors 2 connected in series to, in parallel to or in serial-parallel to one another. The capacitor is provided with: an overvoltage detection circuit 3 for detecting that a voltage applied to the capacitor 2 constituting the capacitor group 11 is larger than a preset value; and a warning signal generation means 13 connected to the overvoltage detection circuit 3, for outputting a signal representing a warning when overvoltage is applied to the capacitor 2 over a preset time, wherein the capacitor can thereby reliably prevent cell deterioration due to overvoltage application to significantly influence the performance of the capacitor device 1 while suppressing excessive warning signal generation to transitional overvoltage and malfunction to noise.