A reactive power compensation device is connected with an AC power system via a switch, and includes an arm circuit having a plurality of sub-modules connected in series, and a central control protection device. Each of the sub-modules includes a DC capacitor, and a bridge circuit for switching whether or not to output a voltage held in the DC capacitor. The central control protection device is configured to shift to a standby mode in which all semiconductor switching elements constituting the bridge circuit of each of the sub-modules are set to an opened state, with the switch being set to a closed state, when the AC power system has a power failure during operation of the reactive power compensation device, and to shift from the standby mode to a stop mode in which the switch is set to an opened state.