A three-level inverter includes a set of series-connected capacitors connected in parallel to a direct-current power supply; two arms connected in parallel to an output of the direct-current power supply and each having an alternating-current output terminal; and a control section having a neutral voltage controller determining a three-phase voltage correction command based on a neutral voltage and voltage of the direct-current power supply, having a coordinate converter converting the three-phase voltage correction command to a voltage correction command on d-q axis, and suppressing voltage variations at the neutral point by correcting a voltage command on d-q axis based on the d-q voltage correction command. The neutral point is connected to one grounded phase of a three-phase grounded power system. The alternating-current output terminals are connected to respective non-grounded phases of the power system. A power conditioner includes the three-level inverter. A power generating system includes the power conditioner.