A voltage control apparatus to be used in a generator system that includes a wind turbine generator having a switching device for controlling a generator; and a capacitor bank for improving power factor provided between the wind turbine generator and a utility grid, the voltage control apparatus characterized by comprising: a control-amount separating means for separating, when it is determined that an interconnection-point voltage (Vr) at an interconnection point where the wind turbine generator is connected to the utility grid deviates from a target value (Vr'), a target control amount for reactive power (Qn) for matching the interconnection-point voltage (Vr) with the target value (Vr') into a first control amount (Q_devi) and a second control amount (Q_shift), the first control amount serving as a control amount for reactive power that is caused by a fluctuation in active power at the interconnection point, the second control amount serving as a control amount for reactive power that is caused by a change in a power flow in the utility grid, the control-amount separating means being configured to: derive a first relationship between the active power (Pn) and the reactive power (Qn) on the basis of the interconnection-point voltage which serves as the target value (Vr'), a bus voltage (Vs), and a power grid impedance (x), said first relationship defining a first curve obtained from: Qn = VsVr ′ 2 x 2 − Pn 2 − Vr ′ 2 x; derive a second relationship between the active power (Pn) and the reactive power (Qn) on the basis of the interconnection-point voltage (Vr) at the interconnection point, the bus voltage (Vs), and the power grid impedance (x), said second relationship differing from the first relationship and defining a second curve obtained from: Qn = VsVr 2 x 2 − Pn 2 − Vr 2 x; and to determine the first control amount (Q_devi) and the second control amount (Q_shift) on the basis of the difference between the first and second relationships, that is, the first control amount (Q_devi) and the second control amount (Q_shift)for matching the second curve with the first curve; the voltage control apparatus further comprising: a wind-turbine control means for controlling the switching device on the basis of the first control amount; and a capacitor-bank control means for controlling the capacitor bank on the basis of the second control amount. derive a first relationship between the active power (Pn) and the reactive power (Qn) on the basis of the interconnection-point voltage which serves as the target value (Vr'), a bus voltage (Vs), and a power grid impedance (x), said first relationship defining a first curve obtained from: Qn = VsVr ′ 2 x 2 − Pn 2 − Vr ′ 2 x; derive a second relationship between the active power (Pn) and the reactive power (Qn) on the basis of the interconnection-point voltage (Vr) at the interconnection point, the bus voltage (Vs), and the power grid impedance (x), said second relationship differing from the first relationship and defining a second curve obtained from: Qn = VsVr 2 x 2 − Pn 2 − Vr 2 x; and to determine the first control amount (Q_devi) and the second control amount (Q_shift) on the basis of the difference between the first and second relationships, that is, the first control amount (Q_devi) and the second control amount (Q_shift)for matching the second curve with the first curve; the voltage control apparatus further comprising: a wind-turbine control means for controlling the switching device on the basis of the first control amount; and a capacitor-bank control means for controlling the capacitor bank on the basis of the second control amount. a wind-turbine control means for controlling the switching device on the basis of the first control amount; and a capacitor-bank control means for controlling the capacitor bank on the basis of the second control amount.