A capacitor unit using a plurality of capacitors and which has a long lifetime and is maintenance-free is provided. The capacitor unit has a high reliability even in harsh using conditions of vibration and shock and a high noise resistant property. This capacitor unit includes a capacitor block in which a plurality of capacitors are incorporated into a holder with body portions of the capacitors sandwiched; a control circuit portion including a charging and discharging circuit for charging or discharging this capacitor block; a relay connector for electrically connecting thereof, and a case housing thereof.