A power conversion control device for controlling a power converting apparatus that includes: a pair of power supply lines (LH, LL); a capacitor provided between said pair of power supply lines; a reactor that forms, with said capacitor, an LC filter that is a choke-input filter; a rectifying unit that rectifies a first AC voltage to be input from a power supply into a DC voltage to output said DC voltage to said LC filter; and a power converting unit that converts, on the basis of a switching signal, a voltage across said capacitor into a second AC voltage, said power conversion control device comprising: a gain setting unit (313A, 313B) that is arranged to set a control gain (k) on the basis of an attenuation coefficient command (ζz) that is a command value of an attenuation coefficient of a transfer function of the voltage across said capacitor to said first AC voltage that is a line-to-line voltage of the AC voltage to be input from the power supply; a voltage control ratio command generating unit that is arranged to correct a command value (K**) of a voltage control ratio by subtracting therefrom a product of said control gain and a voltage across said reactor to output a voltage control ratio command (K*), said voltage control ratio being a ratio of an amplitude of said second AC voltage to an average of said voltage across said capacitor; a switching signal generating unit arranged to generate said switching signal on the basis of said voltage control ratio command; and a power source impedance estimating unit arranged to obtain an estimated value (Z ^) of an impedance on a side of said power source viewed from said rectifying unit, wherein said gain setting unit is arranged to set said control gain (k) using said estimated value, an inductance of said reactor, a capacitance of said capacitor, and said attenuation coefficient command (ζz), and said voltage control ratio command generating unit subtracts from said command value (K**) a product of said control gain and said voltage across said reactor to output said voltage control ratio command (K*), such that the attenuation coefficient of the voltage VC is maintained at the desired attenuation coefficient command (ζz) irrespective of the magnitude of the power source impedance. a pair of power supply lines (LH, LL); a capacitor provided between said pair of power supply lines; a reactor that forms, with said capacitor, an LC filter that is a choke-input filter; a rectifying unit that rectifies a first AC voltage to be input from a power supply into a DC voltage to output said DC voltage to said LC filter; and a power converting unit that converts, on the basis of a switching signal, a voltage across said capacitor into a second AC voltage, said power conversion control device comprising: a gain setting unit (313A, 313B) that is arranged to set a control gain (k) on the basis of an attenuation coefficient command (ζz) that is a command value of an attenuation coefficient of a transfer function of the voltage across said capacitor to said first AC voltage that is a line-to-line voltage of the AC voltage to be input from the power supply; a voltage control ratio command generating unit that is arranged to correct a command value (K**) of a voltage control ratio by subtracting therefrom a product of said control gain and a voltage across said reactor to output a voltage control ratio command (K*), said voltage control ratio being a ratio of an amplitude of said second AC voltage to an average of said voltage across said capacitor; a switching signal generating unit arranged to generate said switching signal on the basis of said voltage control ratio command; and a power source impedance estimating unit arranged to obtain an estimated value (Z ^) of an impedance on a side of said power source viewed from said rectifying unit, a gain setting unit (313A, 313B) that is arranged to set a control gain (k) on the basis of an attenuation coefficient command (ζz) that is a command value of an attenuation coefficient of a transfer function of the voltage across said capacitor to said first AC voltage that is a line-to-line voltage of the AC voltage to be input from the power supply; a voltage control ratio command generating unit that is arranged to correct a command value (K**) of a voltage control ratio by subtracting therefrom a product of said control gain and a voltage across said reactor to output a voltage control ratio command (K*), said voltage control ratio being a ratio of an amplitude of said second AC voltage to an average of said voltage across said capacitor; a switching signal generating unit arranged to generate said switching signal on the basis of said voltage control ratio command; and a power source impedance estimating unit arranged to obtain an estimated value (Z ^) of an impedance on a side of said power source viewed from said rectifying unit, wherein said gain setting unit is arranged to set said control gain (k) using said estimated value, an inductance of said reactor, a capacitance of said capacitor, and said attenuation coefficient command (ζz), and said voltage control ratio command generating unit subtracts from said command value (K**) a product of said control gain and said voltage across said reactor to output said voltage control ratio command (K*), such that the attenuation coefficient of the voltage VC is maintained at the desired attenuation coefficient command (ζz) irrespective of the magnitude of the power source impedance.