A power conversion device comprising: a smoothing capacitor adapted to smooth a direct-current input voltage input from a direct-current power source; an input voltage detection unit adapted to detect a voltage value of the input voltage; a power conversion unit adapted to convert a direct-current voltage smoothed by the smoothing capacitor into an alternating-current voltage to output the alternating-current voltage to a power system; and a controller adapted to control a conversion in the power conversion unit, the controller having a first operation mode of outputting active power to the power system when the voltage value detected by the input voltage detection unit is one of equal to and higher than a determination value, having a second operation mode of outputting reactive power to the power system when the voltage value is lower than the determination value, wherein, when in the first operation mode, the controller is configured to determine whether or not the voltage value is one of equal to and higher than the determination value, wherein, in response to the determination that the voltage value is lower than the determination value, the controller is configured to stop an operation of the first operation mode and start measuring time at the time point when the controller determines that the voltage value is lower than the determination value, the controller being configured to make a transition from the first operation mode to the second operation mode at the time point that a predetermined time elapses, the predetermined time being set in accordance with a capacitance of the smoothing capacitor and a configuration of the power conversion unit such that a voltage of the smoothing capacitor does not become lower than a prescribed value during the predetermined time while the operation of the first operation mode is stopped, and the controller being configured to again perform the first operation mode if the voltage value has been restored to a level equal to or higher than the determination value before said predetermined time has elapsed. a smoothing capacitor adapted to smooth a direct-current input voltage input from a direct-current power source; an input voltage detection unit adapted to detect a voltage value of the input voltage; a power conversion unit adapted to convert a direct-current voltage smoothed by the smoothing capacitor into an alternating-current voltage to output the alternating-current voltage to a power system; and a controller adapted to control a conversion in the power conversion unit, the controller having a first operation mode of outputting active power to the power system when the voltage value detected by the input voltage detection unit is one of equal to and higher than a determination value, having a second operation mode of outputting reactive power to the power system when the voltage value is lower than the determination value, wherein, when in the first operation mode, the controller is configured to determine whether or not the voltage value is one of equal to and higher than the determination value, wherein, in response to the determination that the voltage value is lower than the determination value, the controller is configured to stop an operation of the first operation mode and start measuring time at the time point when the controller determines that the voltage value is lower than the determination value, the controller being configured to make a transition from the first operation mode to the second operation mode at the time point that a predetermined time elapses, the predetermined time being set in accordance with a capacitance of the smoothing capacitor and a configuration of the power conversion unit such that a voltage of the smoothing capacitor does not become lower than a prescribed value during the predetermined time while the operation of the first operation mode is stopped, and the controller being configured to again perform the first operation mode if the voltage value has been restored to a level equal to or higher than the determination value before said predetermined time has elapsed.